Ink jet recording method, ultraviolet curable ink and ink jet recording apparatus

ABSTRACT

An ink jet recording method includes discharging a ultraviolet curable ink of which viscosity is 7 mPa·s or more at 20° C. from a head toward a recording medium, and curing the ultraviolet curable ink adhered to the recording medium, wherein, in the discharging, the temperature of the ultraviolet curable ink discharged is 20 to 30° C., and the viscosity of the ultraviolet curable ink at the temperature is 13 mPa•s or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/851,426, filed Mar. 27, 2013, entitled “Ink Jet Recording Method,Ultraviolet Curable Ink and Ink Jet Recording Apparatus,” which claimspriority to JP Application No. 2012-076469, filed Mar. 29, 2012, JPApplication No. 2012-202377, filed Sep. 14, 2012, and JP Application No.2012-235414, filed Oct. 25, 2012, the disclosures of which areincorporated herein by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to an ink jet recording method, aultraviolet curable ink and an ink jet recording apparatus.

2. Related Art

In the related art, various methods have been used as recording methodsfor forming an image on a recording medium such as paper based on imagedata signals. Among these, an ink jet method has a low running costsince image formation is performed directly on a recording medium bydischarging an ink only to the image area needed using inexpensiveapparatus, and the ink can be used efficiently. Furthermore, an ink jetmethod is excellent as a recording method since noise is low.

In recent years, ink jet recording methods using a ultraviolet curableink in which a polymerizable compound is photopolymerized (cured) byirradiating with ultraviolet have been used in manufacturing a colorfilter, printing to printed circuit boards, plastic cards, vinyl sheets,large billboards and plastic parts, and printing a bar code and datesince an image having excellent scratch resistance and water resistancecan be formed on the recording surface of a recording medium.

For example, JP-A-2009-40880 discloses an ink composition set providedwith an ink composition A1 formed from 2-(vinyloxyethoxy)ethyl acrylateand a hyperbranched polymer, and an ink composition B1 formed from2-(vinyloxyethoxy)ethyl acrylate, a photopolymerization initiator(Irgacure 819 and Irgacure 127 manufactured by Chiba SpecialtyChemicals, Inc.), Pigment Black 7, and a dispersant (a polyoxyalkylenepolyalkylene polyamine) (paragraphs 0083, 0084 and 0087 ofJP-A-2009-40880).

However, there is room for improvement in each ink compositionconstituting the ink composition set disclosed in JP-A-2009-40880 interms of curing properties of the ink, curing wrinkles occurring withthe curing of the ink, and a line width.

SUMMARY

Accordingly, one advantage of some aspects of the invention is toprovide an ink jet recording method using a ultraviolet curable ink thatis excellent in curing, in inhibiting curing wrinkles, and has anexcellent line width. Furthermore, another advantage of some aspects ofthe invention is to provide an ink jet recording method using aultraviolet curable ink that is excellent in inhibiting curing wrinkles,and has an excellent line width. An excellent line width refers to thecharacteristics of the line width becoming thick when the evaluation ofthe line width is performed.

The inventors have found that, as a result of intensive investigations,the above problems can be solved using an ink jet recording methodincluding a discharging step for discharging a predetermined ultravioletcurable ink from a head toward a recording medium, the temperature andviscosity of the ink being in a predetermined range, and a curing stepfor curing the ultraviolet curable ink adhered to the recording medium,and have completed the invention.

That is, the first invention is as follows.

-   [1] An ink jet recording method which includes discharging a    ultraviolet curable ink containing vinyl ether group-containing    (meth)acrylic acid esters represented by the following General    Formula (I), and a monofunctional (meth)acrylate other than the    vinyl ether group-containing (meth)acrylic acid esters, and of which    viscosity is 7 mPa·s or more at 20° C., from a head toward a    recording medium, and curing the ultraviolet curable ink adhered to    the recording medium, wherein, in the discharging, the temperature    of the ultraviolet curable ink discharged is 20 to 30° C., and the    viscosity of the ultraviolet curable ink at the temperature is 13    mPa·s or less,    CH₂═CR¹—COOR²—O—CH═CH—R³  (I)    (In the formula, R¹ is a hydrogen atom or a methyl group, R² is a    divalent organic residue having 2 to 20 carbon atoms, and R³ is a    hydrogen atom or a monovalent organic residue having 1 to 11 carbon    atoms.)-   [2] The ink jet recording method according to [1], wherein recording    is performed by alternately performing main scanning in which the    discharging is carried out while moving the head in the main    scanning direction, and the curing is carried out, and sub-scanning    in which the relative position of the head and the recording medium    is changed in the sub-scanning direction intersecting with the main    scanning direction.-   [3] The ink jet recording method according to [1] or [2], wherein    the monofunctional (meth)acrylate contains a monofunctional    (mech)acrylate having an aromatic ring skeleton.-   [4] The ink jet recording method according to any one of [1] to [3],    wherein there is 40 to 80% by mass of the vinyl ether    group-containing (meth)acrylic acid esters with respect to the total    mass of the ultraviolet curable ink.-   [5] The ink jet recording method according to any one of [1] to [4],    wherein there is 10 to 50% by mass of the monofunctional    (meth)acrylate with respect to the total mass of the ultraviolet    curable ink.-   [6] The ink jet recording method according to any one of [1] to [5],    wherein in the curing, the ultraviolet curable ink is irradiated    with ultraviolet light having irradiation energy of 500 mJ/cm² or    less from a ultraviolet light emitting diode having an emission peak    wavelength in the range of 360 to 420 nm, and the ultraviolet    curable ink is cured.-   [7] The ink jet recording method according to any one of [1] to [6],    wherein, in the curing, the ultraviolet curable ink is irradiated    with ultraviolet light having a peak intensity of 800 mW/cm² or more    from a ultraviolet light emitting diode having an emission peak    wavelength in the range of 360 to 420 nm, and the ultraviolet    curable ink is cured.-   [8] The ink jet recording method according to [2], wherein, when a    unit region that forms dots is employed as a pixel, and an array of    pixels arranged in a main scanning direction is employed as a raster    line, there is a raster line including pixels intended to form a dot    by another main scanning in between raster lines including pixels    intended to form a dot by one main scanning in a sub-scanning    direction, and a plurality of raster lines arranged in the    sub-scanning direction includes a raster line made of pixels    intended to form a dot by a certain main scanning, and pixels    intended not to form a dot by a certain main scanning but form a dot    by another round of main scanning.-   [9] The ink jet recording method according to any one of [1] to [8],    wherein a distance between a nozzle surface of the head and a    recording surface of the recording medium is 5 mm or more.-   [10] A ultraviolet curable ink used in the ink jet recording method    according to any one of [1] to [9].-   [11] An ink jet recording apparatus that performs recording using    the ink jet recording method according to any one of [1] to [8].

Furthermore, the second invention is as follows. [1] An ink jetrecording method which includes discharging a ultraviolet curable ink ofwhich viscosity is 7 mPa·s or more at 20° C. from a head toward arecording medium, and curing the ultraviolet curable ink adhered to therecording medium, wherein, in the discharging, the temperature of theultraviolet curable ink discharged is 20 to 30° C., and the viscosity ofthe ultraviolet curable ink at the temperature is 13 mPa·s or less, andin the curing, the ultraviolet curable ink is cured by irradiating withultraviolet light having a peak intensity of 800 mW/cm² or more from aultraviolet light emitting diode having an emission peak wavelength inthe range of 360 to 420 nm.

-   [2] The ink jet recording method according to [1], wherein recording    is performed by alternately performing main scanning in which the    discharging is carried out while moving the head in the main    scanning direction, and sub-scanning in which the relative position    of the head and the recording medium is changed in the sub-scanning    direction intersecting with the main scanning direction, and the    main scanning includes curing the ultraviolet curable ink adhered to    the recording medium.-   [3] The ink jet recording method according to [1] or [2], wherein a    light source arranged in the main scanning direction of the head is    provided, and recording is performed by alternately performing main    scanning in which the discharging is carried out while moving the    head in the main scanning direction, and sub-scanning in which the    relative position of the head and the recording medium is changed in    the sub-scanning direction intersecting with the main scanning    direction, the main scanning includes curing the ultraviolet curable    ink adhered to the recording medium, a light source is provided at a    downstream side in the sub-scanning direction of the head, and a    curing is further performed after the curing included in the main    scanning.-   [4] The ink jet recording method according to [3], wherein at least    one of the curing included in the main scanning and the curing    further performed after the curing included in the main scanning    includes curing the ultraviolet curable ink by irradiating with    ultraviolet light having a peak intensity of 800 mW/cm² or more from    a ultraviolet light emitting diode having an emission peak    wavelength in the range of 360 to 420 nm.-   [5] The ink jet recording method according to [3] or [4], wherein    the curing further performed after the curing included in the main    scanning includes curing the ultraviolet curable ink by irradiating    with ultraviolet light having a peak intensity of 800 mW/cm² or more    from a ultraviolet light emitting diode having an emission peak    wavelength in the range of 360 to 420 nm, and the curing included in    the main scanning includes curing the ultraviolet curable ink by    irradiating with ultraviolet light having a peak intensity of less    than 800 mW/cm² from a ultraviolet light emitting diode having an    emission peak wavelength in the range of 360 to 420 nm.-   [6] The ink jet recording method according to any one of [1] to [5],    wherein the curing is performed using a plurality of curing, and the    first curing performed after the discharging includes curing the    ultraviolet curable ink by irradiating with ultraviolet light having    a peak intensity of less than 800 mW/cm² from a ultraviolet light    emitting diode having an emission peak wavelength in the range of    360 to 420 nm, and the curing performed after the above curing    includes curing the ultraviolet curable ink by Irradiating with    ultraviolet light having a peak intensity of 800 mW/cm² or more from    a ultraviolet light emitting diode having an emission peak    wavelength in the range of 360 to 420 nm.-   [7] The ink jet recording method according to any one of [1] to [6],    wherein the ink contains 40 to 80% by mass of a monofunctional    (meth)acrylate with respect to the total mass of the ink.-   [8] The ink jet recording method according to any one of [1] to [7],    wherein the ink contains 5 to 45% by mass of a polyfunctional    (meth)acrylate with respect to the total mass of the ink.-   [9] The ink jet recording method according to any one of [1] to [8],    wherein a sum of the irradiation energy due to the curing is 500    mJ/cm² or less.-   [10] The ink jet recording method according to any one of [2] to    [9], wherein, when a unit region that forms dots is employed as a    pixel, and an array of pixels arranged in a main scanning direction    is employed as a raster line, there is a raster line including    pixels intended to form a dot by another main scanning in between    raster lines including pixels intended to form a dot by one main    scanning in a sub-scanning direction, and a plurality of raster    lines arranged in the sub-scanning direction includes a raster line    made of pixels intended to form a dot by a certain main scanning,    and pixels intending not to form a dot by a certain main scanning    and form a dot by another round of main scanning.-   [11] The ink jet recording method according to any one of [1] to    [10], wherein a distance from a nozzle surface of the head to a    surface of the recording medium is 5 mm or more.-   [12] An ink jet recording apparatus that performs recording using    the ink jet recording method according to any one of [1] to [11].-   [13] A ultraviolet curable ink used in the ink jet recording method    according to any one of [1] to [11].

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described with reference to the accompanyingdrawing, wherein like numbers reference like elements.

FIGURE is a schematic diagram of a surrounding of a head of a serialprinter that is one example of the recording apparatus of thisembodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a first embodiment of the invention will be described indetail. In this specification, a “recorded material” refers to formationof a cured material in which an ink is recorded on a recording medium.In addition, a cured material in this specification means a materialcured including a cured film or a coated film.

In addition, in this specification, “cure” refers to an ink beingsolidified by the polymerization of a polymerizable compound when lightis irradiated on an ink that includes a polymerizable compound.“Curable” refers to a property of being cured by being sensitive tolight, and is also referred to as photopolymerizable. A “curing wrinkle”refers to wrinkles occurring on the surface of the coating film aftercuring. A “filling property” is also known as a covering property, andrefers to a property of a recording medium that is underlying being notvisible when viewing a recorded material from the side of a curedmaterial (image) being formed. “Scratch resistance” refers to a propertyof a cured material being difficult to peel off and difficult to becomescratched when rubbing the cured material. “Storage stability” refers toa property of it being difficult for viscosity to change before andafter storage when an ink is stored.

In addition, in this specification, “(meth)acrylate” means at least oneof acrylate and the corresponding methacrylate, “(meth)acrylic” refersto at least one of acrylic and the corresponding methacrylic, and“(meth)acryloyl” refers to at least one of acryloyl and thecorresponding methacryloyl.

Ink Jet Recording Method

One embodiment of the invention relates to an ink jet recording method.The ink jet recording method includes a discharging step for discharginga ultraviolet curable ink having a predetermined composition andphysical properties from a head toward a recording medium, and a curingstep for curing the ultraviolet curable ink adhered to the recordingmedium. In this way, a cured material of the ink is formed by the inkcured on the recording medium.

Recording Medium

Examples of the recording medium described above include anon-ink-absorbent or a low-absorbent recording medium. Among therecording media, examples of the non-ink-absorbent recording mediuminclude those in which plastic is coated or a plastic film is adhered ona substrate such as a plastic film that is not surface treated for inkjet recording (that is, does not form an ink absorbing layer) or paper,or the like. Plastic referred to herein includes polyvinyl chloride(PVC), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene(PS), polyurethane (PU), polyethylene (PE), polypropylene (PP), and thelike. Examples of the low-ink-absorbent recording medium include aprinting paper such as an art paper, a coated paper or a matte paper.

Discharging Step

A discharging step in this embodiment is for discharging a predeterminedultraviolet curable ink (hereinafter simply referred to as “ink”) from ahead toward a recording medium. The viscosity of the ink at 20° C. is 7mPa·s or more. In addition, the temperature of the ultraviolet curableink discharged is 20 to 30° C., and the viscosity of the ultravioletcurable ink discharged is 13 mPa·s or less. Furthermore, the viscosityof the ink at the discharging temperature may be 13 mPa·s or less, andthe viscosity of the ink at 20° C. may or may not be 13 mPa·s or less.

The temperature of 20 to 30° C. described above corresponds to roomtemperature or near room temperature. Thus, if the temperature of theink discharged is room temperature or near room temperature, the costscan be kept low since there is no need for temperature control such asproviding a heating mechanism in a recording apparatus, and anadvantageous effect such as discharge stability becoming favorable dueto little variation in the temperature is obtained.

Furthermore, when the viscosity is 7 mPa·s or more at 20° C., theoccurrence of curing wrinkles can be prevented. It is postulated that,in the film coating of the ink, curing wrinkles occur, when the insideof the coated film is cured later than the surface of the coated filmafter the curing of the surface of the coated film, by the surface ofthe coated film cured earlier being deformed, or the ink inside thecured film irregularly flowing before being cured. Furthermore, it ispostulated that a ultraviolet curable ink having low viscosity shows atendency to have a large polymerization shrinkage associated with curing(the difference between the volume of the ink and the volume of the ink(cured product) after curing with respect to the volume of the inkbefore curing having a predetermined mass), and therefore, theoccurrence of curing wrinkles is significant. In addition, it ispostulated that a ultraviolet curable ink containing vinyl ether-groupcontaining (meth)acrylate represented by General Formula (I) describedbelow is prone to the occurrence of curing wrinkles, and in particular,in a ultraviolet curable ink containing vinyl ether-group containing(meth)acrylate represented by General Formula (I), and having lowviscosity as well, the occurrence of curing wrinkles is significant. Thereason that the occurrence of curing wrinkles is prevented in thisembodiment is postulated to be as follows. While the ink is aultraviolet curable ink containing vinyl ether-group containing(meth)acrylate represented by General Formula (I), viscosity thereof ismaintained in the range described above, therefore, the occurrence ofcuring wrinkles can be reduced. In addition, when the viscosity of theink at the temperature of the ink discharged is 13 mPa·s or less,filling properties becomes excellent. It is postulated that the reasonfor the excellent filling properties is that the increase in viscositydue to temperature decrease, which may happen after discharge when theink is heated can be prevented since the viscosity of the ink is loweven without heating. In this way, in the recording method of thisembodiment, the ultraviolet curable ink can be discharged withoutheating, therefore, advantageous effects can be obtained such that it isnot necessary to provide a mechanism for heating in a recordingapparatus using the recording method. However, the recording apparatusbeing provided with a heating mechanism is not excluded in any way. Inaddition, this embodiment is not limited in any way to the abovepostulations.

In addition, in order to further heighten the advantageous effectsdescribed above, the temperature of the ultraviolet curable inkdischarged is preferably 23 to 28° C., and the viscosity of the ink atthe temperature of the ink discharged is preferably 11 mPa·s or less.The viscosity of the ink at 20° C. is preferably 9 mPa·s or more.

In addition, in the ultraviolet curable ink, viscosity variation due totemperature variation at the time of discharge is large since theultraviolet curable ink has higher viscosity than an aqueous ink used inordinary ink jet inks. Such viscosity variation has large effects on thechanges in droplet sizes and changes in droplet discharging rate, andconsequently can cause image degradation. Therefore, it is preferablethat the temperature of the ink discharged be kept constant as much aspossible. Heating is not necessary in the ultraviolet curable ink ofthis embodiment since the temperature of the ink discharged is roomtemperature or near room temperature, and the temperature of the inkdischarged can be maintained approximately constant. Therefore, theultraviolet curable ink in this embodiment has excellent image quality.

Herein, one example of ink design methods for having the viscosity ofthe ink in a target range will be described.

The mixed viscosity of the entire polymerizable compounds included inthe ink can be calculated from the viscosity of each polymerizablecompound used, and the mass ratio of each corresponding polymerizablecompound with respect to the ink composition.

Assuming that the ink includes polymerizable compounds A, B . . .(omitting the middle) . . . , and N, that is, N types of polymerizablecompounds, the viscosity of the polymerizable compound A is made to beVA, and the mass ratio of the polymerizable compound A with respect tothe total amount of the polymerizable compounds in the ink is made to beMA. The viscosity of the polymerizable compound B is made to be VB, andthe mass ratio of the polymerizable compound B with respect to the totalamount of the polymerizable compounds in the ink is made to be MB.Similarly, the viscosity of the polymerizable compound N is made to beVN, and the mass ratio of the polymerizable compound N with respect tothe total amount of the polymerizable compounds in the ink is made to beMN. Affirmatively, the formula “MA+MB+ . . . (omitting the middle) . . .+MN=1” becomes satisfied. In addition, the mixed viscosity of the entirepolymerizable compounds included in the ink is made to be VX. Then, thefollowing Equation (1) can be assumed to be satisfied.MA×LogVA+MB×LogVB+ . . . (omitting the middle) . . .+MN×LogVN=LogVX  (1)

In addition, for example, when the ink includes two types ofpolymerizable compounds, the mass ratio of the polymerizable compoundslater than MB are set to zero. The number of types of the polymerizablecompounds can be any number of one or more.

Next, one example of a procedure (Steps 1 to 7) to have the viscosity ofthe ink in the desired range will be described.

First, information of the viscosity of each polymerizable compound to beused at a predetermined temperature is obtained (Step 1). The method ofobtaining includes obtaining from manufacturers' catalogs and the like,or measuring the viscosity of each polymerizable compound at apredetermined temperature, and the like. As the viscosity of the singlepolymerizable compound, viscosity information according to themanufacturer of the polymerizable compound to be used can be preferablyemployed since the viscosities sometimes vary depending on themanufacturer even for the same polymerizable compound. Then, the targetviscosity is set as VX, and the composition ratio (mass ratio) of eachpolymerizable compound based on the Formula (1) is determined so that VXbecomes a target viscosity (Step 2). The target viscosity is a viscosityof the ink composition to be obtained ultimately, and is set to anyviscosity within the range of 7 to 13 mPa·s. The predeterminedtemperature is set to any temperature within the range of 20 to 30° C.

Subsequently, the composition of the polymerizable compounds(hereinatter, referred to as “polymerizable composition”) is prepared byactually mixing the polymerizable compounds, and the viscosity at apredetermined temperature is measured (Step 3). Then, if the viscosityof the polymerizable composition is approximately close to a targetviscosity (in Step 4, the viscosity needs to be “target viscosity±5mPa·s”), the viscosity of the ink composition is measured by preparingan ink composition including the polymerizable composition, andcomponents other than the polymerizable compounds such as aphotopolymerization initiator or a pigment (hereinafter, called“components other than the polymerizable compounds”) (Step 4). In Step4, if there is a component mixed with the ink composition in the form ofa pigment dispersion liquid such as pigments as components other thanthe polymerizable compound, the ink composition needs to be prepared inthe mass ratio in which there is subtraction of the mass ratio of thepolymerizable compounds included in the ink composition as the pigmentdispersion liquid from the composition ratio of each polymerizablecompound determined in Step 2, since the polymerizable compoundsincluded in the pigment dispersion liquid in advance are also includedin the ink composition.

Subsequently, the difference between the measured viscosity of thepolymerizable composition and the measured viscosity of the inkcomposition is calculated, and is made to be VY (Step 5). Herein,normally, “VY>0”. VY varies depending on the comprisal conditions suchas types and contents of the components other than the polymerizablecompounds, however, in the examples described below, VY was 2.3 to 3mPa·s.

Subsequently, “target viscosity of Step 2—VY” is defined as VX, and thecomposition ratio of each polymerizable compound is repeatedlydetermined from the above Formula (1) so that VX becomes “targetviscosity of Step 2—VY” defined above (Step 6).

Subsequently, the ink composition is prepared by mixing eachpolymerizable compound having the composition ratio determined in Step 6and the components other than the polymerizable compounds, and theviscosity is measured at a predetermined temperature (Step 7). If theviscosity measured is a target viscosity, the ink composition adjustedin Step 7 is obtained as the ink composition having a target viscosity.

On the other hand, in Step 3, if the measured viscosity of thepolymerizable compounds prepared is not within the range of “targetviscosity±5 mPa·s”, the steps are repeated from step 3 after thefollowing fine adjustment. First, if the measured viscosity is too high,a fine adjustment such as the content of the polymerizable compounds ofwhich viscosity as a single substance is higher than a target viscositybeing reduced, and the content of the polymerizable compounds of whichviscosity as a single substance is lower than a target viscosity beingincreased is carried out. On the other hand, if the measured viscosityis too low, a fine adjustment such as the content of the polymerizablecompounds of which viscosity as a single substance is lower than atarget viscosity being reduced, and the content of the polymerizablecompounds of which viscosity as a single substance is higher than atarget viscosity being increased is carried out. Furthermore, in Step 7,if the measured viscosity of the ink composition prepared is not atarget viscosity, Step 7 is repeated after the same adjustment as theabove fine adjustment is made.

Curing Step

The curing step is for curing the ultraviolet curable ink adhered to therecording medium by irradiating with ultraviolet light (light) from alight source. In this step, initiating species such as radicals, acidsand bases are generated by a photopolymerization initiator included inthe ink being decomposed by the irradiation of ultraviolet light, and aphotopolymerization reaction of the polymerizable compound isfacilitated by the function of the initiating species. Alternatively, inthis step, the photopolymerization reaction of the polymerizablecompound is initiated by the irradiation of ultraviolet light. In thiscase, if a sensitizing dye is present in the ink together with thephotopolymerization initiator, the sensitizing dye in the system absorbsultraviolet light and becomes in an excited state, therefore,facilitating the decomposition of the photopolymerization initiator bybeing in contact with the photopolymerization initiator. As a result, amore sensitive curing reaction can be achieved.

A mercury lamp, a gas or solid-state laser, or the like is mainly usedas a light source (ultraviolet light source), and a mercury lamp and ametal halide lamp are widely known as a light source used for curing aultraviolet curable ink. Meanwhile, being mercury-free has been stronglyrequired in view of current environmental protection, and replacing withGaN-based semiconductor ultraviolet light emitting devices is veryuseful from industrial and environmental viewpoints. In addition, an LED(light emitting diode) such as a ultraviolet light emitting diode(UV-LED) and a ultraviolet laser diode (UV-LD) has a small size, a longlife, a high efficiency, and has a low cost, and is expected as a lightsource for a ultraviolet curable ink.

As a result, in the ultraviolet curable ink of this embodiment, eitheran LED or a metal halide lamp can be suitably used as a light source,however, a UV-LED is preferable among these.

The emission peak wavelength of the above light source (ultravioletlight source) is preferably in the range of 360 to 420 nm, and morepreferably the range of 380 to 410 nm. The emission peak wavelengthbeing within the above range is preferable since an UV-LED has low costalong with being readily obtained.

Furthermore, the peak intensity (peak intensity of irradiation) ofultraviolet light irradiated from a light source having an emission peakwavelength within the above range is preferably 800 mW/cm² or more, andmore preferably 1,000 mW/cm² or more. If the peak intensity ofirradiation is within the above range, curability is more excellent, andthe occurrence of curing wrinkles is more effectively prevented. Moreparticularly, as a result of delayed curing of the inside of the filmcoated with ink compared to the curing of the surface, the surface ofthe film coated with ink is cured first, and the occurrence of curingwrinkles is effectively prevented.

In addition, the value measured using a ultraviolet intensity meterUM-10 and a light receiving unit UM-400 (both manufactured by KonicaMinolta Sensing, Inc.) can be employed as the peak intensity ofirradiation in this specification. However, this does not mean limitingthe method of measuring the peak intensity of irradiation, and measuringmethods known in the related art can be used.

Furthermore, the ultraviolet curable ink that can be cured byirradiation energy of preferably 600 mJ/cm² or less, and more preferably200 to 500 mJ/cm² from a light source having an emission peak wavelengthin the above range can be used in the recording method of thisembodiment. In this case, low cost printing and a high printing speedcan be achieved along with the likely increase of the output of an LED.Herein, when the irradiation is carried out a plurality of times, theirradiation energy is the total irradiation energy that is a sum of eachirradiation energy.

In addition, the irradiation energy in this specification is calculatedby multiplying the irradiation time from the start to the end ofirradiation and the peak intensity of irradiation. Furthermore, when theirradiation is carried out a plurality of times, the irradiation energyis represented by the amount of radiation energy that is a sum of aplurality of radiation. The emission peak wavelength may be one or theplural within the above preferable wavelength range. Even when there ismore than one wavelength, the total amount of irradiation energy ofultraviolet light having a peak emission wavelength of the above rangeis made to be the above irradiation energy.

Such an ink can be obtained by including at least any one of thephotopolymerization initiator decomposed by ultraviolet irradiation inthe above-described wavelength range, and the polymerizable compoundsinitiating polymerization by ultraviolet irradiation in theabove-described wavelength range.

Furthermore, a discharging amount of the ink (application amount,adhering amount) on the recording medium per unit area at the time ofdischarge is preferably 5 to 16 mg/inch² in order to have excellentfilling properties and to prevent unnecessary use of the ink.

In addition, the discharging amount of the ink per unit area variesdepending on recording resolution and the application amount of the inkper recording unit area (pixel) defined by recording resolution, but ispreferably 300 dpi×300 dpi to 1500 dpi×1500 dpi, when the recordingresolution (printing resolution) is represented by “resolution ofsub-scanning direction x resolution of a direction intersecting with thesub-scanning direction (main scanning direction)”. Then it is preferablethat nozzle density of the head and the discharging amount be adjustedin accordance with this recording resolution.

In addition, the discharging amount of the ink per pixel is preferably 2to 200 ng/pixel, and more preferably 3 to 160 ng/pixel. Furthermore, thenozzle density (distance between the nozzles in a nozzle array) ispreferably 180 to 720 dpi, and more preferably 300 to 720 dpi.

Thus, according to this embodiment, an ink jet recording method in whichcurability, suppression of curing wrinkles, and filling properties of asolid pattern image and a line width (main scanning direction andsub-scanning direction) are all excellent can be provided. In addition,hereinafter, the main scanning direction described is sometimes referredto as “transport direction of the recording medium”, and thesub-scanning direction is sometimes referred to as “width direction ofthe recording medium”.

Ink Jet Recording Apparatus

One embodiment of the invention relates to an ink jet recordingapparatus, that is, an ink jet printer. In the recording apparatus, theink jet recording method of the above embodiment can be used. Arecording apparatus (printer) for carrying out the recording method willbe described in detail.

The printer of this embodiment can record ink having different colors ona recording medium (form an image), and examples include an image beingformed using inks of 4 colors of CMYK (cyan, magenta, yellow and black),or an underlying image that provides excellent concealing properties fora recording medium using a white ink being formed.

As the type of a printer of this embodiment, a line printer and a serialprinter are included, or either of them may be used. These havedifferent printing methods. A line printer that is an ink jet recordingapparatus of a line fashion discharges an ink on a recording mediumwhile a head has a nozzle array of the length (approximately)corresponding to the width of the recording medium, and the recordingmedium relatively moves position in the scanning direction intersectingwith the width direction, and recording is performed in one path (singlepath) with the head being fixed without (almost) moving. Meanwhile, aserial printer that is an ink jet recording apparatus of a serialfashion performs recording in normally two paths or more (multi-path)while a head reciprocates (shuttle moves) in a direction perpendicularto the transport direction of the recording medium. In addition, thepath can be paraphrased as “main scanning” described below.

Hereinafter, the printer of this embodiment will be described in moredetail with reference to the drawings. Also, the scope of the inventionis not limited to the following drawings in any way. In addition, ineach drawing used in the following description, the scale of each memberis appropriately changed in order to make the size of each memberidentifiable. FIGURE is a schematic diagram of a surrounding of a headof a serial printer which is one example of the recording apparatus ofthis embodiment.

A carriage unit 80 is a moving mechanism that moves, that is, scans ahead 85 in a direction (hereinafter, referred to as a “moving direction”or a “main-scanning direction”) intersecting with the transportdirection (sub-scanning direction) while discharging the ink, withrespect to the recording medium stationed in a recording area. Thecarriage unit 80 is provided with a carriage 81 and a carriage motor(not shown). In addition, the carriage 81 holds an ink cartridge (notshown) that accommodates a ultraviolet curable ink to be detachable. Thecarriage 81 reciprocates along a guide shaft 82 by the carriage motorwhile being supported on the guide shaft 82 intersecting with thetransport direction described below.

The head 85 is for discharging ultraviolet curable ink with respect tothe recording medium, and has a plurality of nozzles. The head 85 isprovided in the carriage 81, therefore, when the carriage 81 is moved inthe moving direction, the head 85 is also moved in the moving direction.Then, a dot array along the moving direction is formed on the recordingmedium by the head intermittently discharging the ultraviolet curableink while moving in the moving direction. In addition, in moving thehead 85, the ultraviolet curable ink is discharged while the head 85 ismoved from one end to the other end of FIGURE, however, the ultravioletcurable ink is not discharged while the head 85 is moved from the otherend to one end.

The distance between a nozzle surface of the head 85 and a recordingsurface of the recording medium is preferably 0.5 to 20 mm, and morepreferably 1 to 15 mm in order to prevent the contact of the nozzlesurface with the recording medium, and also to prevent shifting of thelanding position of the ink. In particular, recording may be performedunder the condition in which the distance described above is relativelylarge, and the distance in this case is preferably 5 to 20 mm, and morepreferably 5 to 15 mm. The nozzle surface means a surface facing therecording medium in the nozzle plate of the head 85. In thisspecification, when the distance is not constant in the recording areaof the recording medium due to the nozzle surface or the points of therecording surface, the maximum length among the distances between thenozzle surface and the recording surface is called a “distance” betweenthe nozzle surface of the head 85 and the recording surface of therecording medium. In addition, examples of the case in which thedistance is not constant include a case in which recording is performedon a recording medium having irregularities, which is disclosed inJP-A-2000-52596. In this case, it is preferable that recording beperformed under the condition in which the distance described above isrelatively large, and by doing so, recording that prevents the contactof the nozzle surface with the recording medium, and is very suitablefor a recording medium having an irregular surface design can beperformed while simplifying the recording control.

An irradiation unit 90 is for curing the ultraviolet curable ink byirradiating with ultraviolet light with respect to the ultravioletcurable ink adhered (landed) on a recording medium. Dots formed on therecording medium are cured and form a cured material by irradiating withultraviolet light from the irradiation unit 90. The irradiation unit 90includes first irradiation units 92 a and 92 b, and a second irradiationunit 93 at a downstream side in the transport direction of the head 85.

The first irradiation units 92 a and 92 b are for irradiating withultraviolet light to cure the dots formed on the recording medium, andare located in front of the second irradiation unit 93 in which the samecuring is carried out, that is, at an upstream side in the transportdirection.

More specifically, whereas the first irradiation units 92 a and 92 b arefor irradiating with ultraviolet light to preliminarily cure dots formedon the recording medium, the second irradiation unit 93 is forirradiating with ultraviolet light to mainly cure the dots preliminarilycured.

In this specification, “preliminary curing” means temporary fixing(pinning) of the ink, and more particularly, curing prior to main curingto prevent bleeding among the dots or to control the diameter of thedots. In general, the degree of polymerization of the polymerizablecompounds in the preliminary curing is lower than the degree ofpolymerization of the polymerizable compounds in the main curing that iscarried out after the preliminary curing. In addition, “main curing”refers to curing the dots formed on the recording medium to a staterequired to be used as a recorded material.

The second irradiation unit 93 is for irradiating with ultraviolet lightfor curing the dots formed on the recording medium (almost) completely,that is, for main curing. The second irradiation unit 93 is provided ata more downstream side in the transport direction than the head 85, andirradiates with ultraviolet light on the dots formed by the head 85.

In addition, the ink may be mainly cured by irradiating with ultravioletlight from at least one of the first irradiation units 92 a and 92 b andthe second irradiation unit 93. Therefore, the curing step may end byirradiating with ultraviolet light from the second irradiation unit 93without irradiating with ultraviolet light from the first irradiationunits 92 a and 92 b. Furthermore, regardless of ultraviolet light beingirradiated from the second irradiation unit 93, the main curing may beperformed by irradiating with ultraviolet light from at least one of thefirst irradiation units 92 a and 92 b. When the main curing is performedin at least one of the first irradiation units 92 a and 92 b, there maybe no second irradiation unit 93. Thus only main curing may be performedwithout preliminary curing in the curing step.

Thus, in this embodiment, the recording may be performed by alternatelyrepeating the main scanning forming at least a portion of an image whilemoving the head 85 in the moving direction (main scanning direction),thereby discharging ink from the head 85 and curing the ink, and thesub-scanning changing the relative position of the head 85 and therecording medium in the transport direction (sub-scanning direction)intersecting with the main scanning direction. In other words, the mainscanning is for carrying out the discharging step and the curing step,and the sub-scanning is for transporting the recording medium in thetransport direction. Then, it is possible to complete an image on therecording medium by recording that repeats these main scanning andsub-scanning.

Furthermore, instead of the sub-scanning described above, thesub-scanning by the carriage unit 80 being moved in the sub-scanningdirection without transporting the recording medium may be performed.

In addition, the recording method of this embodiment is preferablyperformed by a so-called overlap printing. Herein, the overlap printingin this embodiment will be described.

Overlap printing according to this embodiment includes the followingfirst aspect or second aspect. Herein, a “raster line” means an array(dot array) made of pixels arranged in a single array in the mainscanning direction.

In the first aspect, in one-time main scanning, there are pixels thatform dots and pixels that do not form dots with respect to a singleraster line, and a raster line is present that forms a single rasterline by performing main scanning a plurality of times. Then, a singleraster line can be formed through main scanning a plurality of timesaccording to the first aspect. This aspect can be referred to as an“overlap raster line”. In other words, in the overlap raster line, thereare pixels that form dots in one-time main scanning, and pixels that donot form dots in the one-time main scanning, and form dots in anotherround of main scanning.

The second aspect is that, in addition to the first aspect, there areraster lines that form dots in another round of main scanning in betweenthe raster lines that form dots in one-time main scanning in thesub-scanning direction. In other words, in between the raster lines thatform dots in one-time main scanning, there are also raster lines that donot form dots in the one-time main scanning, and form dots in anotherround of main scanning.

In the overlap raster line described above, the number of paths formingdots is at least two, and may be three or more. In addition to this,among the total number of pixels in one raster line, it is preferablethat 50% or more of pixels that form dots in one path be not adjacent toeach other, and it is more preferable that 70% or more be not adjacentto each other. Moreover, among all the raster lines that form dots, itis preferable that 50% or more be an overlap raster line, and it is morepreferable that 70% or more be an overlap raster line. Among the above,when the overlap printing provided with the second aspect is performed,dots formed in one-time main scanning can be dispersed in the mainscanning direction and the sub-scanning direction.

As a result, according to this embodiment, an ink jet recordingapparatus in which curability, suppression of curing wrinkles, andfilling properties of a solid pattern image and a line width (mainscanning direction and sub-scanning direction) are all excellent can beprovided.

Ultraviolet Curable Ink

Furthermore, one embodiment of the invention relates to a ultravioletcurable ink. The ultraviolet curable ink can be used in the ink jetrecording method and the ink jet recording apparatus of the aboveembodiment. As described above, in the ultraviolet curable ink, theviscosity at 20° C., the temperature at the time of discharge, and theviscosity at the corresponding temperature are in a predetermined range.The ink having the viscosity in a predetermined range can be designed bya calculation from the viscosity and the mass ratio (content ratio) ofeach single polymerizable compound as described above. The viscosity ofthe ink in this embodiment can be measured by using an E-typeviscometer. When using an E-type viscometer, it is in a category ofcommon sense to measure according to the instruction manual of theviscometer, therefore, it is needless to say that the types of a rotoror the rotational speed be set and measured so that the viscosity of theink to be measured can be properly measured in accordance with theinstruction manual, therefore, in this embodiment, it is obvious thatthe viscosity of the ink is set and measured so that the viscosity ofthe ink to be measured can be properly measured in accordance with theinstruction manual.

Hereinafter, additives (components) that are included or may be includedas desired in the ultraviolet curable ink (hereinafter, simply referredto as “ink”) of this embodiment will be described.

Polymerizable Compound

A polymerizable compound included in the ink of this embodiment may curethe ink that is printed by being polymerized during the irradiation oflight either alone or by the action of the photopolymerization initiatordescribed below. The polymerizable compounds contain at least vinylether group-containing (meth)acrylic acid esters represented by GeneralFormula (I), and other monofunctional (meth)acrylates.

Hereinafter, a polymerizable compound will be described in detailfocusing on such (meth)acrylates.

1. Vinyl Ether Group-Containing (Meth)Acrylic Acid Esters

The ink of this embodiment includes vinyl ether group-containing(meth)acrylic acid esters represented by the following General Formula(I) as polymerizable compounds.CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

In the above Formula (I), R¹ is a hydrogen atom or a methyl group, R² isa divalent organic residue having 2 to 20 carbon atoms, and R³ is ahydrogen atom or a monovalent organic residue having 1 to 11 carbonatoms.

By including the vinyl ether group-containing (meth)acrylic acid esters,the ink can have excellent curability, and further have lower viscosity.In detail, it is preferable to use a compound having both a vinyl ethergroup and a (meth)acrylic group in one molecule rather than using acompound having a vinyl ether group and a compound having a(meth)acrylic group separately in order for favorable ink curability.

In General formula (I), the divalent organic residue having 2 to 20carbon atoms represented by R² is preferably a linear, branched orcyclic alkylene group having 2 to 20 carbon atoms, which may besubstituted, an alkylene group having 2 to 20 carbon atoms having anoxygen atom through an ether bond and/or an ester bond in the structure,which may be substituted, and a divalent aromatic group having 6 to 11carbon atoms. Among these, an alkylene group having 2 to 6 carbon atomssuch as an ethylene group, an n-propylene group, an isopropylene groupand a butylene group, or an alkylene group having 2 to 9 carbon atomshaving an oxygen atom through an ether bond in the structure such as anoxyethylene group, an oxy-n-propylene group, an oxyisopropylene groupand an oxybutylene group is preferably used.

In General formula (I), the monovalent organic residue having 1 to 11carbon atoms represented by R³ is preferably a linear, branched orcyclic alkyl group having 1 to 10 carbon atoms, which may besubstituted, and an aromatic group having 6 to 11 carbon atoms, whichmay be substituted. Among these, an alkyl group having 1 or 2 carbonatoms such as a methyl group or an ethyl group, or an aromatic grouphaving 6 to 8 carbon atoms such as a phenyl group and a benzyl group ispreferably used.

When each of the organic residues is a group that may be substituted,the substituents are divided into a group that includes a carbon atomand a group that does not include a carbon atom. First, when thesubstituent is of a group that includes a carbon atom, the carbon atomis counted in the number of carbon atoms of the organic residue.Examples of the group that includes a carbon atom include, but are notlimited to, a carboxyl group or an alkoxy group. Next, examples of thegroup that does not include a carbon atom include, but are not limitedto, a hydroxyl group or a halo group.

Examples of the vinyl ether group-containing (meth)acrylic acid estersinclude, but are not limited to, 2-vinyloxyethyl(meth)acrylate,3-vinyloxypropyl(meth)acrylate, 1-methyl-2-vinyloxyethyl(meth)acrylate,2-vinyloxypropyl(meth)acrylate, 4-vinyloxybutyl(meth)acrylate,1-methyl-3-vinyloxypropyl(meth)acrylate,1-vinyloxymethylpropyl(meth)acrylate,2-methyl-3-vinyloxypropyl(meth)acrylate,1,1-dimethyl-2-vinyloxymethyl(meth)acrylate,3-vinyloxybutyl(meth)acrylate, 1-methyl-2-vinyloxypropyl(meth)acrylate,2-vinyloxybutyl(meth)acrylate, 4-vinyloxycyclohexyl(meth)acrylate,6-vinyloxyhexyl(meth)acrylate,4-vinyloxymethylcyclohexylmethyl(meth)acrylate,3-vinyloxymethylcyclohexylmethyl(meth)acrylate,2-vinyloxymethylcyclohexylmethyl(meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate,2-(vinyloxyethoxy)ethyl(meth)acrylate,2-(vinyloxyisopropoxy)ethyl(meth)acrylate,2-(vinyloxyethoxy)propyl(meth)acrylate,2-(vinyloxyethoxy)isopropyl(meth)acrylate,2-(vinyloxyisopropoxy)propyl(meth)acrylate,2-(vinyloxyisopropoxy)isopropyl(meth)acrylate,2-(vinyloxyethoxyethoxy)ethyl(meth)acrylate,2-(vinyloxyethoxyisopropoxy)ethyl(meth)acrylate,2-(vinyloxyisopropoxyethoxy)ethyl(meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)ethyl(meth)acrylate,2-(vinyloxyethoxyethoxy)propyl(meth)acrylate,2-(vinyloxyethoxyisopropoxy)propyl(meth)acrylate,2-(vinyloxyisopropoxyethoxy)propyl(meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)propyl(meth)acrylate,2-(vinyloxyethoxyethoxy)isopropyl(meth)acrylate,2-(vinyloxyethoxyisopropoxy)isopropyl(meth)acrylate,2-(vinyloxyisopropoxyethoxy)isopropyl(meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)isopropyl(meth)acrylate,2-(vinyloxyethoxyethoxyethoxy)ethyl(meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl(meth)acrylate,2-(isopropenoxyethoxy)ethyl(meth)acrylate,2-(isopropenoxyethoxyethoxy)ethyl(meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy)ethyl(meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl(meth)acrylate,polyethylene glycol monovinyl ether (meth)acrylate, polypropylene glycolmonovinyl ether (meth)acrylate.

Among these, 2-(vinyloxyethoxy)ethyl(meth)acrylate, that is, at leastone of 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate is preferable and 2-(vinyloxyethoxy)ethyl acrylate is morepreferable since the ink can have lower viscosity, a high flash point,and excellent curability. In particular, either of2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate has a simple structure, thereby having a low molecularweight, therefore, it is possible to significantly decrease the inkviscosity. 2-(Vinyloxyethoxy)ethyl(meth)acrylate includes2-(2-vinyloxyethoxy)ethyl(meth)acrylate and2-(1-vinyloxyethoxy)ethyl(meth)acrylate, and 2-(vinyloxyethoxy)ethylacrylate includes 2-(2-vinyloxyethoxy)ethyl acrylate and2-(1-vinyloxyethoxy)ethyl acrylate. In addition, 2-(vinyloxyethoxy)ethylacrylate is better in terms of curability when compared with2-(vinyloxyethoxy)ethyl methacrylate.

The vinyl ether group-containing (meth)acrylic acid esters may be usedeither alone or as a combination of two or more types.

The content of the vinyl ether group-containing (meth)acrylic acidesters, particularly 2-(vinyloxyethoxy)ethyl(meth)acrylate, ispreferably 20 to 90% by mass, more preferably 40 to 80% by mass, andeven more preferably 50 to 75% by mass with respect to the total mass(100% by mass) of the ink. If the content is greater than or equal tothe lower limit, it is possible to decrease the viscosity of the ink,and make curability of the ink more excellent. Meanwhile, if the contentis less than or equal to the upper limit, it is possible to prevent theoccurrence of curing wrinkles more effectively, and a more favorablestorage stability of the ink can be maintained.

Preparation methods of the vinyl ether group-containing (meth)acrylicacid esters include, but are not limited to, a method of esterificationof (meth)acrylic acid and a hydroxyl group-containing vinyl ether(Preparation Method B), a method of esterification of a (meth)acrylicacid halide and a hydroxyl group-containing vinyl ether (PreparationMethod C), a method of esterification of a (meth)acrylic acid anhydrideand a hydroxyl group-containing vinyl ether (Preparation Method D), amethod of transesterification of (meth)acrylic acid esters and ahydroxyl group-containing vinyl ether (Preparation Method E), a methodof esterification of (meth)acrylic acid and a halogen-containing vinylether (Preparation Method F), a method of esterification of an alkali(earth) metal salt of (meth)acrylic acid and a halogen-containing vinylether (Preparation Method G), a method of vinyl exchange of hydroxylgroup-containing (meth)acrylic acid esters and vinyl carboxylate(Preparation Method H), and a method of ether exchange of hydroxylgroup-containing (meth)acrylic acid esters and alkylvinyl ether(Preparation Method I).

Among these, Preparation Method E is preferable since it is possible tofurther exhibit the desired effects of this embodiment.

2. Monofunctional (Meth)Acrylate

The ink of this embodiment also includes a monofunctional (meth)acrylatein addition to the vinyl ether group-containing (meth)acrylic acidesters. By the ink containing the monofunctional (meth)acrylate, thesolubility of a photopolymerization initiator and other additivesbecomes excellent, and discharge stability at the time of ink jetrecording can be easily obtained, and the viscosity of the ink becomeslower, and toughness, heat resistance, and chemical resistance of thecoated film are increased as well.

Examples of the monofunctional (meth)acrylate include phenoxyethyl(meth)acrylate, isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl(meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomyristyl(meth)acrylate, isostearyl (meth)acrylate,2-ethylhexyl-diqlycol(meth)acrylate, 2-hydroxybutyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxy diethylene glycol(meth)acrylate, methoxy polyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate,isobornyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate,lactone-modified flexible (meth)acrylate, t-butylcyclohexyl(meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl(meth)acrylate, benzyl (meth)acrylate, ethoxylated nonylphenyl(meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, andp-cumylphenol EO modified (meth)acrylate.

Among the above, a monofunctional (meth)acrylate having an aromatic ringskeleton in the molecule is preferable since curability, storagestability, and solubility of a photopolymerization initiator are moreexcellent. Examples of the monofunctional (meth)acrylate having anaromatic ring skeleton preferably include, but are not limited to,phenoxyethyl (meth)acrylate, benzyl (meth)acrylate,2-hydroxyphenoxypropyl(meth)acrylate and phenoxy diethylene glycol(meth)acrylate. Among these, at least any one of phenoxyethyl(meth)acrylate and benzyl (meth)acrylate is preferable, and phenoxyethyl(meth)acrylate is more preferable since the viscosity of the ink can bedecreased, and curability, scratch resistance, adhesion and solubilityof a photopolymerization initiator can be all excellent as well.

The monofunctional (meth)acrylate other than the vinyl ethergroup-containing (meth)acrylic acid esters may be used either alone oras a combination of two or more types.

The content of monofunctional (meth)acrylate other than the vinyl ethergroup-containing (meth)acrylic acid esters is preferably 10 to 50% bymass and more preferably 20 to 40% by mass with respect to the totalmass (100% by mass) of the ink. If the content is greater than or equalto the lower limit, the solubility of a photopolymerization initiator aswell as curability becomes more excellent. On the other hand, if thecontent is less than or equal to the upper limit, adhesion as well ascurability becomes more excellent.

3. Polymerizable Compound Other than Above

The ink of this embodiment may further include a polymerizable compoundother than the above (hereinafter, referred to as “other polymerizablecompound”). As the other polymerizable compound, it is possible to usevarious monomers and oligomers such as monofunctional, difunctional, andpolyfunctional such as trifunctional or higher ones known in the relatedart. Examples of the monomers include unsaturated carboxylic acids suchas (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acidand maleic acid or salts thereof, esters, urethanes, amides andanhydrides thereof, acrylonitriles, styrenes, various unsaturatedpolyesters, unsaturated polyethers, unsaturated polyamides andunsaturated urethanes. Examples of the oligomers include an oligomerformed from the monomers described above such as linear acrylicoligomers, epoxy (meth)acrylate, oxetane (meth)acrylate, aliphaticurethane (meth)acrylate, aromatic urethane (meth)acrylate, and polyester(meth)acrylate.

Among the other polymerizable compounds, difunctional or higher estersof (meth)acrylic acid, that is, difunctional or higher (meth)acrylatesare preferable.

Examples of the difunctional (meth)acrylate include diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,dipropylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, EO (ethylene oxide) adduct of bisphenolA di(meth)acrylate, PO (propylene oxide) adduct of bisphenol Adi(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate andpolytetramethylene glycol di(meth)acrylate.

Examples of the trifunctional or higher polyfunctional (meth)acrylateinclude trimethylolpropane tri(meth)acrylate, EO modifiedtrimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, dipentaerythritolhexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerylpropoxy tri(meth)acrylate, caprolactone-modified trimethylolpropanetri(meth)acrylate, pentaerythritolethoxy tetra(meth)acrylate andcaprolactam-modified dipentaerythritol hexa(meth)acrylate.

The other polymerizable compound may be used either alone or as acombination of two or more types.

If the other polymerizable compound is included in the ink, the contentis preferably 15% by mass or less, and more preferably 10% by mass orless with respect to the total mass (100% by mass) of the ink.

Furthermore, it is also possible to omit the addition of aphotopolymerization initiator by using a photopolymerizable compound asa polymerizable compound, however, using a photopolymerization initiatoris preferable in terms that initiation of the polymerization can bereadily adjusted.

Photopolymerization Initiator

The ink of this embodiment may further include a photopolymerizationinitiator. The photopolymerization initiator is used to form printing bycuring the ink present on the surface of the recording medium usingphotopolymerization by the irradiation of ultraviolet light. By usingultraviolet light (UV) among light types, excellence in safety can beobtained, and the costs of a light source lamp can be reduced. Thephotopolymerization initiator that can be used is not limited as long asit generates active species such as radicals or cations by the energy ofultraviolet light, and initiates polymerization of the polymerizablecompound, however, a photo-radical polymerization initiator or aphoto-cationic polymerization initiator may be used, and among these, aphoto-radical polymerization initiator is preferable.

Examples of the photo-radical polymerization initiator include aromaticketones, acylphosphine oxide compounds, aromatic onium salt compounds,organic peroxides, thio compounds (thioxanthone compounds, thiophenylgroup-containing compounds, and the like), hexaarylbiimidazolecompounds, ketoxime ester compounds, borate compounds, aziniumcompounds, metallocene compounds, active ester compounds, compoundshaving a carbon-halogen bond and alkylamine compounds.

Among these, acyl phosphine oxide compounds are preferable since,particularly, the curability of the ink can be more favorable.

Specific examples of the photo-radical polymerization initiator includeacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone,4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether,benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4-diethylthioxanthoneand bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

Examples of commercially available products of the photo-radicalpolymerization initiator include IRGACURE 651(2,2-dimethoxy-1,2-diphenylethan-1-one), IRGACURE 184(1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127(2-hydroxy-1-[4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]phenyl]-2-methyl-propan-1-one),IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone), IRGACURE379(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone),DAROCUR TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide), IRGACURE819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium),IRGACURE OXE 01 (1,2-octanedione,1-[4-(phenylthio)-2-(O-benzoyloxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime)),IRGACURE 754 (a mixture of 2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester ofoxyphenyl acetic acid, and 2-(2-hydroxyethoxy)ethyl ester of oxyphenylacetic acid) (hereinbefore, trade name manufactured by BASFCorporation), KAYACURE DETX-S (2,4-diethylthioxanthone) (trade namemanufactured by Nippon Kayaku Co., Ltd.), Speedcure TPO(2,4,6-trimethylbenzoyldiphenylphosphine oxide), Speedcure DETX(2,4-diethylthioxanthen-9-one) (hereinbefore, trade name manufactured byLambson, Co. Ltd.), Lucirin TPO, LR8893, LR8970 (hereinbefore, tradename manufactured by BASF Corporation), Ebecryl P36 (trade namemanufactured by UCB, Chemicals, Inc.), or the like.

The photopolymerization initiator may be used either alone or as acombination of two or more types. The content of the photopolymerizationinitiator is preferably 20% by mass or less with respect to the totalmass (100% by mass) of the ink in order to have excellent curability byimproving the ultraviolet curing rate, and to avoid coloration derivedfrom the photopolymerization initiator and the remaining melt of thephotopolymerization initiator.

In particular, when the photopolymerization initiator includes anacylphosphine oxide compound, the content of the photopolymerizationinitiator is more preferably 5 to 15% by mass, and even more preferably7 to 13% by mass with respect to the total mass (100% by mass) of theink. If the content is greater than or equal to the lower limit of theabove content, the curability is more excellent. More specifically, thecurability is more excellent since sufficient curing rate can beobtained when curing using an LED particularly (preferable emission peakwavelength: 360 nm to 420 nm). Meanwhile, if the content is less than orequal to the upper limit, the solubility of the photopolymerizationinitiator is even more excellent.

Coloring Material

The ink of this embodiment may further include a coloring material. Asthe coloring material, at least any one of pigments and dyes can beused.

1. Pigment

By using a pigment as a coloring material, the light resistance of theink can be improved. Any one of inorganic pigments and organic pigmentscan be used as the pigment.

As the inorganic pigments, carbon blacks (C.I. Pigment Black 7) such asfurnace black, lamp black, acetylene black and channel black, iron oxideor titanium oxide can be used.

As the organic pigments, azo pigments such as insoluble azo pigments,condensed azo pigments, azo lake and chelate azo pigment, polycyclicpigments such as phthalocyanine pigments, perylene and perinonepigments, anthraquinone pigments, quinacridone pigments, dioxanepigments, thioindigo pigments, isoindolinone pigments and quinophthalonepigments, dye chelates (for example, basic dye-type chelates, acidicdye-type chelates, and the like), dye lakes (basic dye lakes and acidicdye lakes), nitro pigments, nitroso pigments, aniline black or daylightfluorescent pigments may be included.

More specifically, the carbon black used in the black ink includes No.2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100,No. 2200B and the like (hereinbefore, manufactured by MitsubishiChemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500,Raven 1255, Raven 700 and the like (hereinbefore, manufactured byColombian Chemicals Company (Carbon Columbia)), Regal 400R, Regal 330R,Regal 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900,Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 (manufactured byCABOT JAPAN K.K.), Color Black FW1, Color Black FW2, Color Black FW2V,Color Black FW18, Color Black FW200, Color Black S150, Color Black S160,Color Black 3170, Printex 35, Printex U, Printex V, Printex 140U,Special Black 6, Special Black 5, Special Black 4A, Special Black 4(hereinbefore, manufactured by Evonik Degussa GmbH), Microlith Black0066 K (manufactured by formerly Microlith Black C-K, BASF Corporation)and the like.

The pigment used in the white ink includes C.I. Pigment White 6, 18 and21.

The pigment used in the yellow ink includes C.I. Pigment Yellow 1, 2, 3,4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73,74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117,120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172 and 180.

The pigment used in the magenta ink includes C.I. Pigment Red 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30,31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 88, 112,114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177,178, 179, 184, 185, 187, 202, 209, 219, 224 and 245, or C.I. PigmentViolet 19, 23, 32, 33, 36, 38, 43 and 50.

The pigment used in the cyan ink includes C.I. Pigment Blue 1, 2, 3, 15,15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65 and 66, or C.I.Vat Blue 4 and 60.

Examples of other pigments other than the magenta, cyan and yellowpigments include C.I. Pigment Green 7 and 10, C.I. Pigment Brown 3, 5,25 and 26, or C.I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34,36, 38, 40, 43 and 63.

The pigments may be used either alone or as a combination of two or moretypes.

When using the pigment, an average particle diameter thereof ispreferably 300 nm or less, and more preferably 50 to 200 nm. If theaverage particle diameter is within the above range, an image havingexcellent quality can be formed, and more excellent reliability such asdischarge stability and dispersion stability in the ink can be obtainedas well. Herein, the average particle diameter of this specification canbe measured using a dynamic light scattering method.

2. Dye

Dyes can be used as the coloring material. It is possible to use acidicdyes, direct dyes, reactive dyes and basic dyes as the dyes withoutparticular limitation. Examples of the dyes include C.I. Acid Yellow 17,23, 42, 44, 79 and 142, C.I. Acid Red 52, 80, 82, 249, 254 and 289, C.I.Acid Blue 9, 45 and 249, C.I. Acid Black 1, 2, 24 and 94, C.I. FoodBlack 1 and 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132,142, 144 and 173, C.I. Direct Red 1, 4, 9, 80, 81, 225 and 227, C.I.Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199 and 202, C.I. DirectBlack 19, 38, 51, 71, 154, 168, 171 and 195, C.I. Reactive Red 14, 32,55, 79 and 249, or C.I. Reactive Black 3, 4 and 35.

The dyes may be used either alone or as a combination of two or moretypes.

The content of the coloring material is preferably 1 to 20% by mass withrespect to the total mass (100% by mass) of the ink since excellentconcealing properties and color reproducibility can be obtained.

Dispersant

If the ink of this embodiment includes the pigment, it may also includea dispersant for more favorable pigment dispersion. Examples of thedispersant include, but are not limited to, dispersants commonly usedfor preparing a pigment dispersion liquid such as polymeric dispersants.Specific examples thereof include those having one or more types amongpolyoxyalkylene polyalkylene polyamine, vinyl-based polymers andcopolymers, acrylic polymers and copolymers, polyesters, polyamides,polyimides, polyurethanes, amino-based polymers, silicon-containingpolymers, sulfur-containing polymers, fluorine-containing polymers andepoxy resins as main components. Examples of commercially availableproducts of the polymeric dispersant include AJISPER series (trade name)manufactured by Ajinomoto Fine-Techno Co., Inc., SOLSPERSE series(Solsperse 32000, 36000, and the like [hereinbefore, trade name])available from Avecia Inc., DISPERBYK series (trade name) manufacturedby BYK-Chemie GmbH, DISPARLON series (trade name) manufactured byKusumoto Chemicals, Ltd.

The dispersant may be used either alone or as a combination of two ormore types. In addition, the content of the dispersant is notparticularly limited, and a preferable amount may be added asappropriate.

Polymerization Inhibitor

The ink of this embodiment may further include a polymerizationinhibitor. By the ink containing a polymerization inhibitor, apolymerization reaction of the polymerizable compound prior to curingcan be prevented.

The polymerization inhibitor is not particularly limited, however,examples thereof include phenol-based polymerization inhibitors.Examples of the phenol-based polymerization inhibitor include, but arenot limited to, p-methoxyphenol, cresol, t-butyl catechol, di-t-butylparacresol, hydroquinone monomethyl ether, α-naphthol,3,5-di-t-butyl-4-hydroxytoluene, 2,6-di-t-butyl-4-methylphenol,2,2′-methylene-bis(4-methyl-6-t-butylphenol),2,2′-methylene-bis(4-ethyl-6-butylphenol) and4,4′-thio-bis-(3-methyl-6-t-butylphenol).

Examples of commercially available products of the phenol-basedpolymerization inhibitor include p-methoxyphenol (trade namemanufactured by Tokyo Chemical Industry Co. Ltd., p-methoxy phenol),NONFLEX MBP (trade name manufactured by Seiko Chemical Co. Ltd.,2,2′-methylene-bis(4-methyl-6-t-butylphenol)), and BHT SWANOX (tradename manufactured by Seiko Chemical Co. Ltd.,2,6-di-t-butyl-4-methylphenol).

The polymerization inhibitor may be used either alone or as acombination of two or more types. In addition, the content of thepolymerization inhibitor is not particularly limited, and a preferableamount may be added as appropriate.

Surfactant

The ink of this embodiment may further include a surfactant. Thesurfactant is not particularly limited, however, for example,polyester-modified silicone or polyether-modified silicone can be usedas a silicone-based surfactant, and using polyether-modifiedpolydimethylsiloxane or polyester-modified polydimethylsiloxane isparticularly preferable.

Commercially available products of the surfactant include BYK-347,BYK-348, BYK-UV3500, 3510, 3530, 3570 (hereinbefore, manufactured byBYK-Chemie GmbH).

The surfactant may be used either alone or as a combination of two ormore types. In addition, the content of the surfactant is notparticularly limited, and a preferable amount may be added asappropriate.

Other Additives

The ink of this embodiment may include additives (components) other thanthe additives described above. Such components are not particularlylimited, however, examples thereof include a polymerization accelerator,a penetration enhancer, a wetting agent (a moistener), and otheradditives known in the related art. Examples of the other additivesdescribed above include a fixing agent, a mold proof agent, anantiseptic agent, an antioxidant, a ultraviolet absorber, a chelatingagent, a pH adjusting agent and a viscosity agent known in the relatedart.

Thus, according to this embodiment, a ultraviolet curable ink havingexcellent storage stability, which is used in an ink jet recordingmethod in which curability, suppression of curing wrinkles, fillingproperties of a solid pattern image, and a line width (main scanningdirection and sub-scanning direction) are all excellent can be provided.

Hereinafter, a second embodiment for implementing the invention will bedescribed in detail. In addition, the details described above in thefirst embodiment can be applied to the second embodiment, except for thedetails described below. Furthermore, among the details of the secondembodiment described below, the details that can be applied to the firstembodiment described above may be applied to the first embodiment.

Ink Jet Recording Method

One embodiment of the invention relates to an ink jet recording method.The ink jet recording method includes a discharging step for discharginga ultraviolet curable ink having predetermined properties from a headtoward a recording medium, and a curing step for curing the ultravioletcurable ink adhered to the recording medium. In addition, the ink jetrecording method of the invention may be an ink jet recording methodperformed by using an ink jet recording apparatus of this embodimentdescribed above or below.

Discharging Step

A discharging step in this embodiment is for discharging a predeterminedultraviolet curable ink from a head toward a recording medium(hereinafter simply referred to as “ink”). The viscosity of the ink at20° C. is 7 mPa·s or more. In addition, the temperature of theultraviolet curable ink discharged is 20 to 30° C., and the viscosity ofthe ultraviolet curable ink discharged is 13 mPa·s or less. Furthermore,the viscosity of the ink at the discharging temperature may be 13 mPa·sor less, and the viscosity of the ink at 20° C. may or may not be 13mPa·s or less.

The temperature of 20 to 30° C. described above corresponds to roomtemperature or near room temperature. Thus, if the temperature of theink discharged is room temperature or near room temperature, the costscan be kept low since there is no need for temperature control such asproviding a heating mechanism in a recording apparatus, and anadvantageous effect such as discharge stability becoming favorable dueto little variation in the temperature is obtained.

Furthermore, when the viscosity is 7 mPa·s or more at 20° C., theoccurrence of curing wrinkles can be prevented. It is postulated that,in the film coating of the ink, curing wrinkles occur, when the insideof the coated film is cured later than the surface of the coated filmafter the surface of the coated film is cured, by the surface of thecoated film cured earlier being deformed, or the ink inside the curedfilm irregularly flowing before being cured. Furthermore, it ispostulated that a ultraviolet curable ink having low viscosity shows atendency to have a large polymerization shrinkage associated with curing(the difference between the volume of the ink and the volume of the ink(cured product) after curing with respect to the volume of the inkbefore curing having a predetermined mass), and therefore, theoccurrence of curing wrinkles is significant. In addition, when theviscosity of the ink at the temperature of the ink discharged is 13mPa·s or less, filling properties becomes excellent. It is postulatedthat the reason for these excellent filling properties is that theincrease in viscosity due to temperature decrease, which may happenafter discharge when the ink is heated can be prevented since theviscosity of the ink is low even without heating. In this way, in therecording method of this embodiment, the ultraviolet curable ink can bedischarged without heating, therefore, advantageous effects can beobtained such that it is not necessary to provide a mechanism forheating in a recording apparatus using the recording method. However,the recording apparatus being provided with a heating mechanism is notexcluded in any way. In addition, this embodiment is not limited in anyway to the above postulations.

In addition, in order to further heighten the advantageous effectsdescribed above, the temperature of the ultraviolet curable inkdischarged is preferably 23 to 28° C., and the viscosity of the ink atthe temperature of the ink discharged is preferably 11 mPa·s or less.The viscosity of the ink at 20° C. is preferably 9 mPa·s or more.

In addition, in the ultraviolet curable ink, viscosity variation due totemperature variation at the time of discharge is large since theultraviolet curable ink has higher viscosity than an aqueous ink used inordinary ink jet inks. Such viscosity variation has large effects on thechanges in droplet sizes and changes in droplet discharging rate, andconsequently can cause image degradation. Therefore, it is preferablethat the temperature of the ink discharged be kept constant as much aspossible. Heating is not necessary in the ultraviolet curable ink ofthis embodiment since the temperature of the ink discharged is roomtemperature or near room temperature, and the temperature of the ink tobe discharged can be maintained approximately constant. Therefore, theultraviolet curable ink in this embodiment has excellent image quality.

Curing Step

The curing step is for curing the ultraviolet curable ink adhered to therecording medium by irradiating with ultraviolet light (light) from alight source. The curing step of the first embodiment described abovecan be used as the curing step, but in the second embodiment, the curingstep includes at least a curing step performed by irradiation having apeak intensity (peak intensity of irradiation) of 800 mW/cm² or morefrom a light emitting diode having an emission peak wavelength in therange of 360 to 420 nm.

In addition, the peak intensity (peak intensity of irradiation) ofultraviolet light irradiated from a light source having an emission peakwavelength within the above range is preferably 1,000 mW/cm² or more. Ifthe peak intensity of irradiation is within the above range, curabilityis more excellent, and the occurrence of curing wrinkles is moreeffectively prevented. More particularly, as a result of delayed curingof the inside of the coating ink compared to the curing of the surface,the surface of the coating ink is cured first, and the occurrence ofcuring wrinkles is effectively prevented.

In addition, the value measured using a ultraviolet intensity meterUM-10 and a light receiving unit UM-400 (both manufactured by KonicaMinolta Sensing, Inc.) can be employed as the peak intensity ofirradiation in this specification.

Furthermore, the ultraviolet curable ink that can be cured byirradiation energy of preferably 600 mJ/cm² or less, more preferably 500mJ/cm² or less, and even more preferably 200 to 500 mJ/cm² from a lightsource having an emission peak wavelength in the above range can be usedin the recording method of this embodiment. In addition, it ispreferable that irradiation energy be set in the above range. In thiscase, low cost printing and a high printing speed can be achieved alongwith the likely increase of the output of an LED. Herein, when theirradiation is carried out a plurality of times, the irradiation energyis the total irradiation energy that is a sum of each irradiationenergy. Furthermore, when irradiation is carried out a plurality oftimes, at least any one of the curing steps has only to include a curingstep performed by irradiation having a peak intensity (peak intensity ofirradiation) of 800 mW/cm² or more from a light emitting diode having anemission peak wavelength in the range of 360 to 420 nm.

Ink Jet Recording Apparatus

One embodiment of the invention relates to an ink jet recordingapparatus, that is an ink jet printer. The recording apparatus can usethe ink jet recording method of the above embodiment. The recordingapparatus described above can be used as the recording apparatus(printer) for carrying out the recording method. The recording apparatusperforms the curing step with respect to the ink adhered to therecording medium with at least one light source being provided, however,it is preferable that the recording apparatus be provided with a lightsource arranged in the main scanning direction of the head, and a lightsource disposed further downstream in the sub-scanning direction thanthe head in terms that it is possible to perform a curing step includedin the main scanning, and a further curing step after the main scanning.A light source disposed further downstream in the sub-scanning directionthan the head may be disposed in the recording apparatus separately fromthe carriage mounted with the head, however, it is preferable that alight source be mounted on the carriage mounted with the head in termsthat the curing step can be performed by moving the carriage in the mainscanning direction. In this case, the light source arranged in the mainscanning direction of the head and the light source disposed furtherdownstream in the sub-scanning direction than the head may beintegrated.

When irradiation on the ink (curing step) is carried out a plurality oftimes, at least any one of the curing steps includes a curing stepperformed by irradiation having a peak intensity (peak intensity ofirradiation) of 800 mW/cm² or more from a light emitting diode having anemission peak wavelength in the range of 360 to 420 nm. The peakintensity of irradiation is preferably 1,000 mW/cm² or more, and ispreferably 2,000 mW/cm² or less, although the upper limit is notlimited. If the peak intensity of irradiation is in the above range,reduction of curing wrinkles becomes excellent. Furthermore, irradiationenergy of the curing step (the sum when the curing step is performed aplurality of times) performed by irradiation having a peak intensity(peak intensity of irradiation) of 800 mW/cm² or more from a lightemitting diode having an emission peak wavelength in the range of 360 to420 nm is preferably 600 mJ/cm² or less, and more preferably 500 mJ/cm²or less. The lower limit is preferably 100 mJ/cm² or more, and morepreferably 200 mJ/cm² or more in terms of sufficient curing.

Among these, it is preferable that the curing step performed after thecuring step included in the main scanning by the light source disposedfurther downstream in the sub-scanning direction than the head include acuring step performed by irradiation having a peak intensity (peakintensity of irradiation) of 800 mW/cm² or more from a light emittingdiode having an emission peak wavelength in the range of 360 to 420 nm.The reason is that the higher the peak intensity, the greater theirradiation energy when irradiation time is constant, and increasing theirradiation energy of the final curing step performed later can ensuresufficient curing of the ink.

Meanwhile, the curing step included in the main scanning may include acuring step performed by irradiation having a peak intensity (peakintensity of irradiation) of 800 mW/cm² or more from a light emittingdiode having an emission peak wavelength in the range of 360 to 420 nm,however, including a curing step performed by irradiation having a peakintensity (peak intensity of irradiation) of less than 800 mW/cm² from alight emitting diode having an emission peak wavelength in the range of360 to 420 nm is preferable in terms that it can reduce uneven luster ofthe recorded image and power consumption of the light source arranged inthe main scanning direction of the head. In the curing step included inthe main scanning, the peak intensity (peak intensity of irradiation) ispreferably 500 mW/cm² or less, more preferably 50 to 500 mW/cm², andeven more preferably 200 to 500 mW/cm². In addition, the irradiationenergy of the curing step included in the main scanning is preferably500 mJ/cm² or less, more preferably 10 to 500 mJ/cm², even morepreferably 10 to 200 mJ/cm², and even more preferably 10 to 100 mJ/cm².In addition, the sum of the irradiation energy of all the curing stepsis preferably 600 mJ/cm² or less, and more preferably 500 mJ/cm² orless, and the lower limit is preferably 100 mJ/cm² or more, and morepreferably 200 mJ/cm² or more in terms of sufficient curing.

When performing a curing step a plurality of times, the curing stepincluded in the main scanning is the first curing step after thedischarging step, and the curing step after the curing step included inthe main scan is a curing step after the first curing step. The ink jetrecording method of this embodiment may also be performed using a lineprinter. In case of a line printer, a light source may be disposed at adownstream side in the recording medium transport direction of the headin the direction of recording width of the recording medium with alength greater than the recording width. There may be a plurality oflight sources disposed, and in this case, the curing step by the lightsource closest to the head is the first curing step after thedischarging step, and the curing step after is a curing step after thefirst curing step.

It is preferable that the ink jet recording apparatus of this embodimentperform recording using overlap printing described above in terms of aline width, and suppression of curing wrinkles. The overlap printingdescribed above can be considered as a recording method in which, when aunit region that forms dots is employed as a pixel, and an array ofpixels arranged in a main scanning direction is employed as a rasterline, there is a raster line including pixels intended to form a dot byanother main scanning in between raster lines including pixels intendedto form a dot by one main scanning in a sub-scanning direction, and aplurality of raster lines arranged in the sub-scanning directionincludes a raster line made of pixels intended to form a dot by acertain main scanning, and pixels intending not to form a dot by acertain main scanning and form a dot by another round of main scanning.Herein, intended to form a dot in certain pixels by a certain mainscanning refers to forming dots in certain pixels by a certain mainscanning when pixel data are the data that form dots in certain pixelscorresponding to the image to be recorded. Whether or not dots areactually formed in the pixels intended to form a dot depends on theimage data corresponding to certain pixels in, but, if the areas havingan image is an image area of high concentration, the image data becomesdata that form dots in almost all the pixels in the region, therefore,in such a region, being intended to form a dot in certain pixels by acertain main scanning is forming dots in certain pixels by a certainmain scanning, and both are essentially the same.

Ultraviolet Curable Ink

Furthermore, one embodiment of the invention relates to a ultravioletcurable ink. The ultraviolet curable ink can be used in the ink jetrecording method and the ink jet recording apparatus of the aboveembodiment. As described above, in the ultraviolet curable ink, theviscosity at 20° C., the temperature at the time of discharge, and theviscosity at the corresponding temperature are in a predetermined range.The ink having the viscosity in a predetermined range can be designed bya calculation from the viscosity and the mass ratio (content ratio) ofeach single polymerizable compound as described above.

Hereinafter, additives (components) that are included or may be includedas desired in the ultraviolet curable ink (hereinafter, simply referredto as “ink”) of this embodiment will be described.

Polymerizable Compound

The ultraviolet curable ink of this embodiment includes a polymerizablecompound. Among the polymerizable compounds, including 40 to 80% by massof the above-described monofunctional (meth)acrylate is preferable, andincluding 50 to 70% by mass is more preferable with respect to the totalmass of the ink in terms of curability, decreasing viscosity andreducing curing wrinkles. Herein, the ink of this embodiment may notinclude the above-described vinyl ether group-containing (meth)acrylicacid esters, and when it does, content thereof is included in thecontent of the above-described monofunctional (meth)acrylate.

Furthermore, if the ink includes the vinyl ether group-containing(meth)acrylic acid esters, the content is preferably 20 to 90% by mass,more preferably 40 to 80% by mass, and even more preferably 50 to 75% bymass with respect to the total mass (100% by mass) of the ink. If thecontent is within the above range, decreasing the viscosity of the ink,and curability of the ink can be more favorable. In addition, the ink ofthis embodiment may include difunctional or higher (meth)acrylates, andcontent thereof is preferably 5 to 45% by mass, and more preferably 10to 40% by mass with respect to the total mass of the ink in termscurability, storage stability and decreasing viscosity of the ink.

The types of polymerizable compound used may be the same as those in thefirst embodiment described above, however, among these, phenoxyethyl(meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate,2-(2-vinyloxyethoxy)ethyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, tetrahydrofurfuryl (meth)acrylate ordicyclopentenyloxyethyl (meth)acrylate is preferable as a monofunctional(meth)acrylate. Dipropylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, tripropylene glycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, or trifunctional or higher (meth)acrylateshaving a pentaerythritol skeleton or a dipentaerythritol skeleton ispreferable as a polyfunctional (meth)acrylate. For the components otherthan the polymerizable compound, the same components as those used inthe ink of the first embodiment described above can be used.

In addition, in this specification, the ultraviolet curable ink used inthe ink jet recording method of this embodiment is a ultraviolet curableink sold for an ink jet recording apparatus that performs recordingusing the ink jet recording method of this embodiment, and theultraviolet curable ink used in the ink jet recording apparatus of thisembodiment is a ultraviolet curable ink sold for the ink jet recordingapparatus of this embodiment.

EXAMPLES Examples of First Embodiment

Hereinafter, the first embodiment will be described in detail usingexamples and comparative examples, however, the invention is not limitedto these examples.

Materials Used

Materials used in the examples and the comparative examples are asfollows.

Polymerizable Compound

-   -   VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, trade name        manufactured by Nippon Shokubai Co., Ltd., monofunctional        (meth)acrylate, and hereinafter described as “VEEA”.)    -   Viscoat #192 (phenoxyethyl acrylate, trade name manufactured by        Osaka Organic Chemical Industry Ltd., monofunctional        (meth)acrylate, and hereinafter described as “PEA”.)    -   V #160 (benzyl acrylate, trade name manufactured by Osaka        Organic Chemical Industry Ltd., monofunctional (meth)acrylate,        and hereinafter described as “BZA”.)    -   IBXA (isobornyl acrylate, trade name manufactured by Osaka        Organic Chemical Industry Ltd., monofunctional (meth)acrylate,        and hereinafter described as “IBX”.)    -   SR508 (dipropylene glycol diacrylate, difunctional        (meth)acrylate, trade name manufactured by Sartomer Company        Inc.)    -   A-DPH (dipentaerythritol hexaacrylate, hexafunctional        (meth)acrylate, trade name manufactured by Shin-Nakamura        Chemical Co., Ltd., and hereinafter described as “A-DPH”.)        Polymer

Viscoat #1000 (manufactured by Osaka Organic Chemical Industry Ltd., ahyperbranched polymer, viscosity 273 mPa·s, number of acrylic groups 14,and hereinafter described as “V#1000”.)

-   In addition, Viscoat #1000 is a hyperbranched polymer in which    functional groups are branched from dipentaerythritol as a core, and    contains ethylene glycol diacrylate as a diluent monomer.    Photopolymerization Initiator

IRGACURE 819 (trade name manufactured by BASF Corporation, solid content100%, and hereinafter described as “819”.)

-   -   DAROCUR TPO (trade name manufactured by Lambson, Co. Ltd., and        hereinafter described as “TPO”.)        Surfactant

BYK-UV3500 (polyether-modified polydimethylsiloxane, manufactured byBYK-Chemie GmbH, and hereinafter described as “BYK3500”)

Coloring Material

C.I. Pigment Black 7 (manufactured by Mitsubishi Chemical Corporation,Mitsubishi Carbon MA11, and hereinafter described as “PB-7”.)

Dispersant

Solsperse 32000 (trade name manufactured by Avecia Inc., and hereinafterdescribed as “SOL32000”.)

Polymerization Inhibitor

p-Methoxyphenol (trade name manufactured by Tokyo Chemical Industry Co.,Ltd., p-methoxyphenol, and hereinafter described as “MEHQ”.)

Preparation of Ultraviolet Curable Inks 1 to 9

Ultraviolet Curable Inks 1 to 9 were obtained by adding each of thematerials shown in Table 1 so that contents thereof (unit: % by mass)were those shown in Table 1, and stirring the mixture using a high-speedwater-cooled stirrer.

Measurement and Evaluation Items

1. Rank of Ink Viscosity at 20° C.

The viscosity of each ink prepared as above was measured at 20° C. usinga DVM-E type rotary viscometer (manufactured by Tokyo Keiki Inc.). Acone for a DVM-E type having a cone angle of 1°34′ and a cone radius of2.4 cm was used as a rotor. A rotation speed was set to 10 rpm.

The evaluation criteria were as follows. The evaluation results areshown in Table 1 below.

-   1: Less than 7 mPa·s.-   2: Greater than or equal to 7 mPa·s and less than or equal to 13    mPa·s.-   3: Greater than 13 mPa·s.-   2. Evaluation of Storage Stability of Ink

Each of the inks prepared as above was placed in a 50 cc glass vial, andafter sealing, these glass vials were placed in a thermostatic chamberat 60° C. and were allowed to stand for 7 days. After taking out thevials after 7 days, and returning the vials to room temperaturesufficiently, the viscosity at 20° C. was measured in the same manner asthat in the “Rank of Ink Viscosity at 20° C.”. Then the viscosityincrease ratio of the viscosity after standing for 7 days was calculatedwith respect to the initial (immediately after preparation) viscosity.

The evaluation criteria were as follows. The evaluation results areshown in Table 1 below.

-   A: +5% or less.-   B: Greater than +5%.-   3. Evaluation of Ink Curability

Each of the above inks was applied on Lumirror #125-E20 (trade namemanufactured by Toray Industries Inc., PET film) using a bar coatermanufactured by Tester Sangyo Co., Ltd. The thickness of the film afterthe curing of the coated film was 10 μm. Next, the ink coated film curedby irradiating with ultraviolet light having illuminance of 1,000 mW/cm²from an LED (Firefly [trade name], manufactured by Phoseon Technology)having a peak wavelength of 395 nm on the ink applied for apredetermined time was obtained. After the irradiation, the surface ofthe above ink coated film was rubbed back and forth 20 times using acotton swab manufactured by Johnson & Johnson K.K under the conditionsof a load of 130 g, and irradiation energy required until no scratchmark showed was measured.

The evaluation criteria were as follows. The evaluation results areshown in Table 1 below.

-   A: 200 mJ/cm² or less.-   B: Greater than 200 mJ/cm² and less than or equal to 300 mJ/cm².-   C: Greater than 300 mJ/cm².

TABLE 1 Ultraviolet Curable Inks 1 to 9 No. of Ultraviolet Curable InkComponent Name Name 1 2 3 4 5 6 7 8 9 Polymerizable VEEA(1) 50.0 20.087.7 77.7 82.7 — 42.7 60.0 55.0 Compound PEA(1) 30.0 30.0 — — 5.0 42.7 —— 15.0 BZA(1) — — — — — — — 20.0 — IBX(1) — — — — — — — — 10.0 SR508(2)— 30.0 — — — 45.0 45.0 — — A-DPH(6) 7.7 7.7 — — — — — 7.7 7.7 PolymerV#1000 — — — 10.0 — — — — — Photopolymer- 819 4.0 4.0 4.0 4.0 4.0 4.04.0 4.0 4.0 ization TPO 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 InitiatorSurfactant BYK 3500 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 ColoringMaterial PB-7 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Dispersant SOL 320001.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Polymerization MEHQ 0.1 0.1 0.1 0.10.1 0.1 0.1 0.1 0.1 Inhibitor Total 100.0 100.0 100.0 100.0 100.0 100.0100.0 100.0 100.0 Rank of Ink Viscosity at 20° C. 2 3 1 2 1 2 2 2 2Storage Stability A A B B A A B A A Curability A A A C A C C A B

In addition, in Table 1, the numbers of each polymerizable compound inparentheses represent the number of functional groups of the(meth)acrylate. In addition, Ultraviolet Curable Inks 1, 8 and 9correspond to the inks that can be used in examples, and UltravioletCurable Inks 2 to 7 correspond to the inks used in comparative examples.

In Table 1, it was found that the ultraviolet curable inks (No. 1, 2, 8and 9) that contain vinyl ether group-containing (meth)acrylic acidesters represented by General Formula (I), and a monofunctional(meth)acrylate other than the vinyl ether group-containing (meth)acrylicacid esters, and also, have the viscosity of 7 mPa·s or more at 20° C.were excellent in both storage stability and curability of the ink whencompared to otherwise ultraviolet curable inks.

In detail, first, the curability of the ultraviolet curable ink becomesexcellent by the ultraviolet curable ink including vinyl ethergroup-containing (meth)acrylic acid esters. In addition, at least thestorage stability becomes excellent, and furthermore, the curability maybecome excellent as well by the ultraviolet curable ink including amonofunctional (meth)acrylate other than the vinyl ethergroup-containing (meth)acrylic acid esters. Furthermore, the viscosityof the ultraviolet curable ink at 20° C. being 7 mPa·s or more caneffectively prevent the occurrence of curing wrinkles as describedbelow. Then, the viscosity of the ultraviolet curable ink at thedischarging temperature being 13 mPa·s or less can especially make theline width excellent (filling properties of line width to be morespecific) as described below. In addition, when comparing UltravioletCurable Inks 1, 8 and 9 with each other, the curability of the inkbecomes more excellent when using PEA or BZA as a monofunctional(meth)acrylate other than the vinyl ether group-containing (meth)acrylicacid esters compared to when using IBX. Hereinafter, recording methodsin each of the examples and comparative examples will be described.

Recording Method 1 Examples 1 to 3, 7 and 8, and Comparative Examples 1to 8

A serial printer shown in FIGURE was used. More specifically, using anink jet printer PX-G5000 (manufactured by Seiko Epson Corporation), alight source (UV-LED) described below was installed further downstreamin the sub-scanning direction than a carriage and a platen of thisprinter. In addition, a heater capable of heating the ink was installedin the head so that the temperature of the ink at the time of dischargecould be adjusted. The head was filled with one of each ink composition.Printing was performed by carrying out main scanning while the ink wasdischarged from the head on a white PET film (Lumirror 125E20manufactured by Toray Industries Inc.) that was the recording medium.The nozzle density in the sub-scanning direction of the nozzle arrayused for printing was set to 360 dpi.

When carrying out the main scanning, the ultraviolet curable ink landedand adhered on the recording medium by the main scanning waspreliminarily cured per one path (one-time main scanning), using an LEDhaving a peak wavelength of 395 nm, which was mounted on the side of thecarriage (irradiation was carried out on the dots). At this time,Firefly (peak intensity of irradiation 1,000 mW/cm²) was used as the LEDmounted on the side of the carriage. In addition, irradiation energy inthe irradiation of one path was set to 100 mJ/cm².

Next, the main scanning and the sub-scanning were alternately repeatedby performing the following main scanning after performing asub-scanning that transported the recording medium in the sub-scanningdirection intersecting with the main scanning direction.

After the completion of the printing (after completion of the last mainscanning), uncured ink was cured completely by further irradiating theultraviolet curable ink from the light source (the same type as thosemounted on the carriage) corresponding to the width of the recordingmedium provided separately with the carriage on the recording mediumtransported more downstream in the sub-scanning direction than theplaten. The irradiation energy of the curing was 400 mJ/cm². Elaboratingon the recording conditions (printing conditions), the number of paths(number of main scannings) was set to “two paths (main scanningdirection)×two paths (sub-scanning direction)=four paths”. In detail,overlap printing that forms dots on every other pixel of the firstraster line in one path was performed so that there was one raster linethat forms dots by another main scanning in between two raster linesthat form dots in one-time main scanning. The distance between thenozzle surface and the recording surface of the recording medium was setto 1 mm. In addition, the recording resolution (sub-scanningdirection×main scanning direction) was set to 720 dpi×720 dpi.

Furthermore, the temperature of the ink at the time of discharge was asshown in the following Table 2 and Table 3, respectively. Thetemperature was a value obtained by measuring the temperature of anozzle plate having the nozzle plate provided with a thermocouple. Inother words, the temperature of the ink to be discharged from the nozzleof the head corresponds to the temperature of the nozzle plate(hereinafter the same). Furthermore, in the example in which the inktemperature at the time of discharge was 35° C. among the temperatureslisted in Tables 2 and 3, the ink at the time of discharge was heated to35° C. using a temperature adjustment mechanism (heater) mounted on thehead. In addition, in the examples in which the temperature of the inkat the time of ink was other than 35° C., the printing was performed atroom temperature without the use of a temperature control mechanism sothat the temperature remained at room temperature. In each example, thedischarging amount was made to be the same between each example and eachcomparative example by adjusting the voltage of a head-driving waveform.

Recording Method 2 Example 4, and Comparative Examples 9 and 10

Recording was carried out in the same manner as that of Recording Method1 except that the number of paths was changed to “one path (mainscanning direction)×two paths (sub-scanning direction)=two paths”. Inother words, Recording Method 2 was different from Recording Method 1,overlap printing was not performed since one path was made to be in themain scanning direction, and dots were formed on all the pixels of oneraster line in one path. In addition, regarding the heating by thetemperature control mechanism carried out in Comparative Example 9,heating was carried out in the same manner as that of ComparativeExamples 3 and 9 and using Recording Method 1.

Recording Method 3 Example 5, and Comparative Examples 11 and 12

Recording was carried out in the same manner as that of Recording Method1 except that the distance between the nozzle surface and the recordingsurface of the recording medium was changed to 10 mm. In addition,regarding the heating by temperature control mechanism carried out inComparative Example 11, heating was carried out in the same manner asthat of Comparative Examples 3 and 9 and using Recording Method 1.

Recording Method 4 Example 6, and Comparative Examples 13 and 14

Recording was carried out in the same manner as that of Recording Method1 except the following. Recording was carried out in one path (singlepath) using a line printer equipped with a line head corresponding tothe width of the recording medium disclosed in FIG. 2 ofJP-A-2011-184610. In addition, the nozzle density of the line head wasset to 720 dpi. Herein, the transport direction of the recording mediumis the main scanning direction. The same light source with the lightsource provided further downstream in the sub-scanning direction thanthe platen using Recording Method 1 was provided more downstream in thetransport direction than the line head, and irradiation was performedusing the corresponding light source. In addition, regarding the heatingby temperature control mechanism carried out in Comparative Example 13,heating was carried out in the same manner as that of ComparativeExamples 3 and 9 and using Recording Method 1.

Measurement and Evaluation Items

1. Rank of Ink Viscosity at Time of Discharge

The viscosity of each ink was measured in the same manner as the rank ofink viscosity at 20° C. described above except that the temperatureduring the viscosity measurements was set to the ink temperature at thetime of discharge listed in Tables 2 and 3. In addition, the evaluationcriteria were the same as the criteria of the rank of ink viscosity at20° C. described above.

2. Evaluation of Filling Properties of Solid Pattern Image

A solid pattern image having a recording resolution of 720 dpi×720 dpiand a dimension (size) of 20 cm×20 cm was recorded by forming and curingdots of 11 ng/pixel in each pixel on the recording medium. The pixel isa minimum recording unit area defined by recording resolution. Then,whether or not the recording surface not hidden by the dots in the areaof the solid pattern image was visible was evaluated visually at adistance of 30 cm from the recording medium. In addition, the “solidpattern image” means, typically, an image pattern that should have animage in which the recording surface is not seen since the recordingarea of the recording medium is covered with ink by dots being recordedfor all the pixels in the pixels that are a minimum recording unit areadefined by recording resolution. The evaluation criteria were asfollows. The evaluation results are shown in Table 2 and Table 3 below.

-   A: The recording surface was not seen.-   B: The recording surface was seen.    3. Evaluation of Line Width

The line width was measured by forming dots of 11 ng/pixel in each pixelof one pixel array arranged in the sub-scanning direction and the mainscanning direction, and recording a line made of dot arrays. Measurementand evaluation of the line width was separated into the case ofrecording dot arrays in the sub-scanning direction, and the case ofrecording dot arrays in the main scanning direction.

The evaluation criteria were as follows. The evaluation results areshown in Table 2 and Table 3 below. In the table, “line width,sub-scanning direction” means a line width when recording a dot array inthe sub-scanning direction, and “line width, main scanning direction”means a line width when recording a dot array in the main scanningdirection.

-   A: 110 μm or more-   B: Greater than or equal to 80 μm and less than 110 μm-   C: Greater than or equal to 50 μm and less than 80 μm-   D: Less than 50 μm    4. Evaluation of Curing Wrinkles

Each solid image pattern obtained in “2. Evaluation of FillingProperties of Solid Pattern Image” was used. The root mean square height(Rq value) of each solid pattern image was measured using a lasermicroscope VK-9700 (manufactured by Keyence Corporation). In addition,the surface of each solid pattern image was observed visually. Theevaluation criteria were as follows. The evaluation results are shown inTable 2 and Table 3 below.

-   A: Rq was 4 or less. Luster was seen on the surface of the solid    pattern image.-   B: Rq was greater than 4 and less than or equal to 6. A slight    luster was seen on the surface of the solid pattern image.-   C: Rq was greater than 6. No luster was seen on the surface of the    solid pattern image.

TABLE 2 Examples 1 to 8, and Comparative Examples 1 to 4 Item/No.Example Comparative Example of Examples 1 2 3 4 5 6 7 8 1 2 3 4 No. ofInk Used 1 8 9 1 1 1 1 1 3 2 2 3 Temperature 25° C. 25° C. 25° C. 25° C.25° C. 25° C. 30° C. 20° C. 35° C. 30° C. 35° C. 25° C. of Ink at Timeof Discharge Rank of Ink 2 2 2 2 2 2 2 2 1 3 2 1 Viscosity at Time ofDischarge No. of 1 1 1 2 3 4 1 1 1 1 1 1 Recording Method Filling A A AA A A A A A — B A Properties (Solid Pattern) Line Width A A A A A B A AA — C A (Sub-scanning Direction) Line Width A A A B A B A A A — C A(Main Scanning Direction) Curing A A A B A B A A C — A C wrinkles

TABLE 3 Comparative Examples 5 to 14 Item/No. of Examples 5 6 7 8 9 1011 12 13 14 No. of Ink Used 4 5 6 7 2 3 2 3 2 3 Temperature of Ink at25° C. 25° C. 25° C. 25° C. 35° C. 25° C. 35° C. 25° C. 35° C. 25° C.Time of Discharge Rank of Ink Viscosity 2 1 2 2 2 1 2 1 2 1 at Time ofDischarge No. of Recording 1 1 1 1 2 2 3 3 4 4 Method Filling PropertiesA A A A B A B A B A (Solid Pattern) Line Width A A A A C A D A D B(Sub-scanning Direction) Line Width A A A A D B D A D B (Main ScanningDirection) Curing wrinkles B C A A B C A C B C

From the above results, it was found that, in the ink jet recordingmethod (each example) in which the steps of discharging and curing theultraviolet curable ink including vinyl ether group-containing(meth)acrylic acid esters represented by General Formula (I), and amonofunctional (meth)acrylate other than the vinyl ethergroup-containing (meth)acrylic acid esters are included, and theviscosity of the ultraviolet curable ink at 20° C. is 7 mPa·s or more,the temperature at the time of discharge is 20 to 30° C., and theviscosity of the ultraviolet curable ink at the correspondingtemperature is 13 mPa·s or less, the curability, the suppression ofcuring wrinkles and the line width were all excellent, and fillingproperties of the solid pattern image were also excellent compared tothose of otherwise ink jet recording methods (each comparativeexamples). Hereinafter, a discussion will be described based on theabove results, however, the discussion does not limit the scope of theinvention.

First, in Comparative Example 2, the evaluation results were notdescribed since the number of nozzles that did not discharge were morethan half of the total number of nozzles when discharging InkComposition 2 at the temperature of 30° C., and it was determined asnon-dischargeable. It is postulated that Ink Composition 2 is an inkthat is not suitable for discharging when the discharging temperature isset to 30° C. In addition, in Comparative Example 3, it is postulatedthat the filling properties were poor since the viscosity had beenincreased due to the decrease in ink temperature during the period afterthe ink was discharged and before the ink was landed on the recordingmedium even when the ink was made to be dischargeable by reducing theviscosity of the ink by heating. This also can be postulated from thefact that, when the filling properties, the line width (sub-scanningdirection), and the line width (main scanning direction) were evaluatedin the same manner as that of Comparative Example 3 except that thewhole ink jet printer was installed in a temperature-controlled room,and the temperature-controlled room was set to 35° C., the evaluationresults were all A. In addition, it was postulated that making the inkdischargeable by reducing the ink viscosity by heating the ink cannot beconsidered as preferable since it facilitates the erosion of the headdue to the ink of members constituting the head by using a heated inkheated as well as needing a temperature adjustment mechanism, and thedurability of the head tends to be reduced. Furthermore, the occurrenceof curing wrinkles was significant in Comparative Examples 1, 4, 6, 10,12 and 14. It is postulated that the occurrence of curing wrinkles wassignificant in all the ink compositions used in these comparativeexamples due to the fact that the viscosity of the ink was less than 7mPa·s at 20° C., and the viscosity of the ink was low as described abovetogether with the ink including vinyl ether group-containing(meth)acrylic acid esters represented by General Formula (I). Inaddition, the reason for the curability of the ink being poor inComparative Examples 5 and 7 is the same as described above.

In addition, the relationship between the evaluation results and therecording method will be discussed. In Example 1 using Recording Method1 by overlap printing, any of the line width (main scanning direction)and the suppression of curing wrinkles were found to be more excellentcompared to those of Example 4 using Recording Method 2 that does notdepend on overlap printing. It is postulated that, in the line width(main scanning direction) in Example 4, a phenomenon was observed inwhich dots did not spread since dots adjacently formed in the mainscanning direction in one path attracted each other, therefore, the linewidth deteriorated. In addition to this, it is postulated that theresult of curing wrinkles worsened due to the occurrence of a thickportion in the dots due to the dots attracting each other. Furthermore,in the line width of the sub-scanning direction, it was identified thatthere was no change regardless of the use of overlap printing sincethere was no possibility of forming adjacent dots in one path.

In addition, it was postulated that the reason for a very poorevaluation result in the line width in Comparative Example 11 (RecordingMethod 3) in which the distance between the nozzle surface and therecording surface of the recording medium surface was made to be largeat 10 mm compared to that of Comparative Example 3 in which RecordingMethod 1 was performed (distance 1 mm) using the same Ink 2 was becauseof further viscosity increase due to further ink temperature decreasebefore the ink reached the recording medium. Furthermore, in Example 1using Recording Method 1 using a serial printer, any of the solidpattern image, filling properties of the line width (sub-scanningdirection and main scanning direction), and suppression of curingwrinkles was found to be more excellent compared to those of Example 6using Recording Method 4 using a line printer. The reason is postulatedsuch that, in the line printer, the adjacent dots attracted each otherto form adjacent dots in one path in any direction of the transportdirection (main scanning direction) of the recording medium and thewidth direction (sub-scanning direction) of the recording medium,therefore, the line width and the like was inferior in Example 6.

Furthermore, separately, curing was carried out using a metal halidelamp replacing an LED, and the result of curing wrinkles became morefavorable overall, however, the deformation of the recording medium wasobserved due to the heat generated from the light source. In addition tothis, the light source became larger and thereby power consumption wasincreased due to the use of a metal halide lamp. As a result, theinventors confirmed that using an LED was more preferable than using ametal halide lamp.

Example of Second Embodiment

Hereinafter, the second embodiment will be described in detail usingexamples and comparative examples, however, the invention is not limitedto these examples. The compositions used in the adjustment of the inkadjustment examples, the materials used, adjustment method of the ink,measurement and evaluation items of this embodiment were the same asthose used in the examples of the first embodiment described above.

Evaluation of Recording Test

A recording test was performed and evaluated in the same manner as thatof Recording Methods 1 to 4 in the examples of the first embodimentdescribed above except that the recording method was performed under therecording conditions described below using the following Serial Ink JetPrinter 2 as the recording apparatus. Serial Ink Jet Printer 2 was thesame as the serial ink jet printer used in the examples of the firstembodiment (referred to as Serial Ink Jet Printer 1) except for thefollowing. One more LED having a peak wavelength of 395 nm that was thesame type as the LED mounted on the side of the head as the Light Source2 further downstream in the sub-scanning direction than the head of thecarriage was mounted. The length of the sub-scanning direction of theLight Source 2 was made to be the same as the length of the sub-scanningdirection of the head. The two LEDs mounted next to the left and rightsides of the head in the same manner as those in a Serial Ink JetPrinter 1 were employed as Light Source 1. The light source providedfurther downstream in sub-scanning direction than the platen separatelyfrom the carriage was not used in irradiation by turning off the power.The peak intensity of irradiation of Light Source 1 and Light Source 2was set to values listed in Tables 5 and 6 for each example by adjustingthe input current values, respectively. The irradiation energy near onepath per one LED 1 of the Light Source 1, and Light Source 2,respectively, was 100 mJ/cm² in the examples in which the peak intensityof irradiation was 1,000 mW/cm². The nozzle density of the head was 360dpi, and the number of nozzles was 360.

Recording Method 4 was the same as Recording Method 1 except that thenumber of paths (number of main scannings) was set to one path (mainscanning direction)×one path (sub-scanning direction)=one path” bycompleting the discharging step of the area having the length of thedistance of the head in the sub-scanning direction of the recordingmedium in one path with the distance in one-time sub-scanning directionas the distance of one sub-scanning one-time of the head, using theabove Serial Ink Jet Printer 2 in which the head was changed to thathaving the nozzle density of 720 dpi and the number of nozzles 720. Asthe evaluation criteria, the following evaluation of uneven luster wasperformed in addition to the items described above. The evaluationresults are shown in Tables 4 and 5.

Evaluation of Uneven Luster

Each solid pattern image obtained in 2. Evaluation of Filling Propertiesof Solid Pattern Image described above was used. When a light reflectionon the image was seen with the image at an angle in which the reflectedlight of a fluorescent lamp of the ceiling could be seen, the luster ofthe sub-scanning direction at the time of recording of the image wasdifferent, that is, the luster of the main scanning direction wasconstant, therefore, the boundary of the area in which the luster of thesub-scanning direction was different being recognized as a line (lusterbanding) extending in the main scanning direction was visually observed.The evaluation criteria were as follows.

-   A: The line extending in the main scanning direction was seen.-   B: The line extending in the main scanning direction was not seen.

TABLE 4 Item/No. of Example Examples. 1 2 3 4 5 6 7 8 9 10 11 12 13 14No. of Ink Used. 1 8 9 1 1 1 1 1 4 6 7 1 1 8 Irradiation 1000 1000 10001000 1000 1000 1000 1000 1000 1000 1000 800 500 500 Intensity of LightSource 1 (mW/cm²) Irradiation Intensity 1000 1000 1000 1000 1000 10001000 1000 1000 1000 1000 800 1000 1000 of Light Source 2 (mW/cm²)Temperature of 25 25 25 25 25 25 30 20 25 25 25 25 25 25 Ink at Time ofDischarge (° C.) Rank of Ink 2 2 2 2 2 2 2 2 2 2 2 2 2 2 Viscosity atTime of Discharge No. of Recording 1 1 1 2 3 4 1 1 1 1 1 1 1 1 MethodFilling Properties A A A A A A A A A A A A A A (Solid Pattern) LineWidth A A A A A B A A A A A A A A (Sub-scanning Direction) Line Width AA A B A B A A A A A A A A (Main Scanning Direction) Curing wrinkles A AA B A B B A A B A A B B Uneven Luster B B B B B B B B B B B B A A

TABLE 5 Item/No. Comparative Example of Examples 1 2 3 4 5 6 7 8 9 10 1112 13 14 No. of Ink Used. 3 2 2 3 5 2 3 2 3 2 3 1 8 2 IrradiationIntensity 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 500 500500 of Light Source 1 (mW/cm²) Irradiation Intensity 1000 1000 1000 10001000 1000 1000 1000 1000 1000 1000 500 500 500 of Light Source 2(mW/cm²) Temperature of Ink 35 30 35 25 25 35 25 35 25 35 25 25 25 35 atTime of Discharge (° C.) Rank of Ink 1 3 2 1 1 2 1 2 1 2 1 2 2 2Viscosity at Time of Discharge No. of Recording 1 1 1 1 1 2 2 3 3 4 4 11 1 Method Filling Properties A — B A A B A B A B A A A A (SolidPattern) Line Width (Sub- A — C A A C A D A D B A A C scanningDirection) Line Width (Main A — C A A D B D A D B A A C ScanningDirection) Curing wrinkles C — A C C B C A C B C C C B Uneven Luster B BB B B B B B B B B A A A

From the above results, it was found that, in the ink jet recordingmethod which included the discharging step for discharging theultraviolet curable ink of which viscosity was 7 mPa·s or more at 20° C.from the head toward the recording medium, and the step for curing theultraviolet curable ink adhered to the recording medium, wherein, in thedischarging step, the temperature of the ultraviolet curable inkdischarged was 20 to 30° C., and the viscosity of the ultravioletcurable ink at the temperature was 13 mPa·s or less, and in the curingstep, the ultraviolet curable ink was cured by irradiating withultraviolet light having a peak intensity of 800 mW/cm² or more from aultraviolet light emitting diode having an emission peak wavelength inthe range of 360 to 420 nm, the filling properties of the solid patternimage, the line width, and suppression of curing wrinkles were allexcellent compared to those of otherwise ink jet recording methods.Hereinafter, a discussion will be described based on the above results,however, the discussion does not limit the scope of the invention in anyway. In addition, the discussion described above also applies regardingthe examples having the same contents as the examples and thecomparative examples of the first embodiment.

In Comparative Example 3, it is postulated that the filling propertieswere poor since the viscosity had been increased due to the decrease inink temperature during the period after the ink was discharged andbefore the ink was landed on the recording medium even when the ink washeated to 35° C., however, a tendency of the filling properties and theline width being not constant was also seen during the test depending onthe degree of viscosity increase of the ink due to a decrease in the inktemperature, therefore, it was not preferable. In Comparative Examples12 to 14 that did not include the curing step for curing the ultravioletcurable ink by irradiating with ultraviolet light having a peakintensity of 800 mW/cm² or more from a ultraviolet light emitting diodehaving an emission peak wavelength in the range of 360 to 420 nm, atendency of inferior suppression of curing wrinkles was seen. It ispostulated that curing wrinkles had occurred on the ink surface when theinside of the ink was cured since the curing of the inside of thecoating ink was delayed compared to the curing of the surface of the inkwhile the ink was cured gradually by irradiating with ultraviolet lightof weak intensity.

Examples 13 and 14 were examples including a curing step using LightSource 1 that cured the ultraviolet curable ink by irradiating withultraviolet light having a peak intensity of 800 mW/cm² or more from aultraviolet light emitting diode having an emission peak wavelength inthe range of 360 to 420 nm, and a curing step using Light Source 1 thatwas the first irradiation (curing step) after the ink being landed onthe recording medium, and cured the ultraviolet curable ink byirradiating with ultraviolet light having a peak intensity of less than800 mW/cm², however, in Examples 13 and 14, the suppression of curingwrinkles was slightly inferior but favorable, and it was favorable inhaving no uneven luster compared to that of other examples in which thepeak intensity in the curing step using Light Source 1 was 800 mW/cm² ormore. The reason for this has not been fully elucidated, however, it ispostulated that, if the peak intensity of irradiation of the firstirradiation was less than 800 mW/cm², the curing step was performed inwhich the dots having the surface of the ink that had landed by theearlier main scanning had not completely cured, and the dots landedoverlapping with the earlier dots by the next main scanning wereirradiated simultaneously, and it was difficult for the level differenceof the ink surface of the boundary to remain, therefore, uneven lusterreduced. In Example 6, and Comparative Examples 10 and 11 usingRecording Method 4, uneven luster in the sub-scanning direction (lineextending in the main scanning direction) was seen with an interval ofthe distance of the head in the sub-scanning direction. In the examplesrecording using Recording Methods 1 to 3 in which uneven luster wasseen, uneven luster was seen with an interval shorter than the distanceof the head in the sub-scanning direction. In addition, in the examplesin which the evaluation of curing wrinkles was C, the difference ofluster could be observed as uneven luster in the evaluation of unevenluster that observed the reflected light on the image.

The entire disclosure of Japanese Patent Application No. 2012-235414,filed Oct. 25, 2012 and 2012-76469, filed Mar. 29, 2012 and 2012-202377,filed Sep. 14, 2012 are expressly incorporated by reference herein.

What is claimed is:
 1. An ink jet recording method comprising:discharging an ultraviolet curable ink of which viscosity is 7 mPa·s ormore at 20° C., from a head toward a recording medium; and curing theultraviolet curable ink adhered to the recording medium by irradiatingthe ultraviolet curable ink with ultraviolet light having a peakintensity of 800 mW/cm² or more and 2000 mW/cm² or less from anultraviolet light emitting diode having an emission peak wavelength inthe range of 360 to 420 nm, wherein recording is performed byalternately performing main scanning in which the ink is dischargedwhile moving the head in the main scanning direction and cured, andsub-scanning in which the relative position of the head and therecording medium is changed in the sub-scanning direction, whichintersects with the main scanning direction; wherein, when a unit regionthat forms dots is employed as a pixel, and an array of pixels arrangedin a main scanning direction is employed as a raster line, there is araster line including pixels intended to form a dot by another mainscanning in between raster lines including pixels intended to form a dotby one main scanning in a sub-scanning direction, and a plurality ofraster lines arranged in the sub-scanning direction includes a rasterline made of pixels intended to form a dot by a certain main scanning,and pixels intended not to form a dot by a certain main scanning butform a dot by another round of main scanning; and wherein the recordingmethod is performed by using an ink jet recording apparatus, the ink jetrecording apparatus is lacking a heating mechanism for controlling atemperature of the ultraviolet curable ink during discharging.
 2. Theink jet recording method according to claim 1, wherein, in the curing,ultraviolet light having irradiation energy of 500 mJ/cm² or less froman ultraviolet light emitting diode having an emission peak wavelengthin the range of 360 to 420 nm is irradiated, and the ultraviolet curableink is cured.
 3. The ink jet recording method according to claim 1,wherein a distance between a nozzle surface of the head and a recordingsurface of the recording medium is 5 mm or more.
 4. The ink jetrecording method according to claim 1, wherein a light source arrangedin the main scanning direction of the head is provided, and recording isperformed by alternately performing main scanning in which thedischarging is carried out while moving the head in the main scanningdirection, and sub-scanning in which the relative position of the headand the recording medium is changed in the sub-scanning directionintersecting with the main scanning direction, the main scanningincludes curing the ultraviolet curable ink adhered to the recordingmedium, a light source is provided at a downstream side in thesub-scanning direction of the head, and a curing is further performedafter the curing included in the main scanning.
 5. The ink jet recordingmethod according to claim 1, further comprising a first curing performedafter the discharging that includes curing the ultraviolet curable inkby irradiating with ultraviolet light having a peak intensity of lessthan 800 mW/cm² from a ultraviolet light emitting diode having anemission peak wavelength in the range of 360 to 420 nm.
 6. The ink jetrecording method according to claim 1, wherein the ink contains 40 to80% by mass of a monofunctional (meth)acrylate with respect to the totalmass of the ink.
 7. The ink jet recording method according to claim 1,wherein the ink contains 5 to 45% by mass of a polyfunctional(meth)acrylate with respect to the total mass of the ink.
 8. The ink jetrecording method according to claim 1, wherein a sum of the irradiationenergy due to the curing is 500 mJ/cm² or less.
 9. The ink jet recordingmethod according to claim 1, wherein the ultraviolet curable inkcontaining vinyl ether group-containing (meth) acrylic acid estersrepresented by the following general formula (I),CH₂═CR¹—COOR²—O—CH═CH—R³   (I) in the formula R¹ is a hydrogen atom or amethyl group, R² is a divalent organic residue having 2 to 20 carbonatoms, and R³ is a hydrogen atom or a monovalent organic residue having1 to 11 carbon atoms.